When Leila swapped the s9 DSM for s1, I discovered the disdrometer messages were broken. The quick summary is that the eeprom got erased, leading to these questions.  The details follow.

It looks like the first data file at setup for s1 is s1_20200325_120000.dat. Disdrometer was working as of 2020-03-25,17:49:13. I'm guessing the site was setup that day, and for whatever reason the disdrometer data messages start there, without the boot messages. Probably the time was not synchronized until then.

[isfs@barolo raw_data]$ data_stats -a -i 1,-1 s1_20200325_120000.dat 
2020-04-29,09:39:54|NOTICE|parsing: /h/eol/isfs/isfs/projects/SWEX/ISFS/config/swex.xml
Exception: EOFException: s1_20200325_120000.dat: open: EOF
sensor                           dsm sampid    nsamps |------- start -------|  |------ end -----|    rate        minMaxDT(sec) minMaxLen
s1:/dev/ttyDSM1                    1      8       371 2020 03 25 17:49:13.254  03 25 23:59:10.090    0.02      57.007   60.021 4142 4142
s1:/dev/gps_pty0                   1     10     44573 2020 03 25 17:48:16.892  03 25 23:59:59.024    2.00      -2.133    1.253   59  147
s1:/var/log/chrony/tracking.log    1     18      2654 2020 03 25 17:48:16.958  03 25 23:59:59.913    0.12       0.000 2578.788  100  100
s1:/dev/ttyDSM2                    1     20     22436 2010 02 01 00:00:57.185  03 25 23:59:59.275    0.00-1946506.446    1.342   42   44
s1:/dev/ttyDSM3                    1     22         0 ***********************  ******************     nan         nan      nan  nan  nan
s1:/dev/ttyDSM4                    1     40    446122 2010 02 01 00:00:57.159  03 25 23:59:59.974    0.00-1946507.325    0.493   60   60
s1:/dev/ttyPWRMONV                 1     60    445799 2010 02 01 00:00:56.308  03 25 23:59:59.422    0.00-1946506.527    1.172    3   90
s1:/dev/ttyDSM5                    1    100    223047 2020 03 25 17:48:17.032  03 25 23:59:59.976   10.00      -2.889    0.428   32   32
s1:/dev/ttyDSM7                    1 0x8000      4467 2020 03 25 17:48:20.498  03 25 23:59:57.411    0.20       1.616    5.689   26   60

The messages appeared to be fine, including reporting the serial number 450620:

2020 03 25 17:49:13.2549       0  1,   8    4142 450620;0000.000;00;20000;024;27025;00000;0;000;...

It booted up again 2020-03-26,01:35:11, for reasons unknown. It reported one good message, then started rebooting and reporting "POWERSUPPLY TEST FAILED !!!".

2020-04-29,09:13:52|INFO|opening: s1_20200326_013511.dat
2020 03 26 01:35:11.6336   121.6  1,   8       3 \r\n
2020 03 26 01:35:11.6346 0.001042  1,   8      22 BOOTLOADER PARSIVEL\r\n
2020 03 26 01:35:12.9390   1.304  1,   8       3 \r\n
2020 03 26 01:35:12.9400 0.001042  1,   8      21 *** PARSIVEL 2 ***\r\n
2020 03 26 01:35:12.9518 0.01182  1,   8      20 OTT HYDROMET GMBH\r\n
2020 03 26 01:35:12.9631 0.01129  1,   8      22 COPYRIGHT (C) 2019 \r\n
2020 03 26 01:35:12.9755 0.01238  1,   8      18 VERSION: 2.11.6\r\n
2020 03 26 01:35:12.9843 0.008857  1,   8      17 BUILD: 2112151\r\n
2020 03 26 01:35:13.0045 0.02015  1,   8       3 \r\n
2020 03 26 01:35:13.3090  0.3045  1,   9      40          0          0      20000         15          0          0          3          0          0          0 
2020 03 26 01:35:13.3090       0  1,   8    4142 450620;0000.000;00;.....;\r\n
2020 03 26 01:35:28.0125    14.7  1,   8       4 \x80\r\n
2020 03 26 01:35:29.6423    1.63  1,   8      22 BOOTLOADER PARSIVEL\r\n
2020 03 26 01:35:30.9507   1.308  1,   8       3 \r\n
2020 03 26 01:35:30.9517 0.001042  1,   8      21 *** PARSIVEL 2 ***\r\n
2020 03 26 01:35:30.9635 0.01181  1,   8      20 OTT HYDROMET GMBH\r\n
2020 03 26 01:35:30.9748 0.01131  1,   8      22 COPYRIGHT (C) 2019 \r\n
2020 03 26 01:35:30.9858 0.01094  1,   8      18 VERSION: 2.11.6\r\n
2020 03 26 01:35:30.9961 0.01028  1,   8      17 BUILD: 2112151\r\n
2020 03 26 01:35:31.0044 0.008336  1,   8       3 \r\n
2020 03 26 01:35:35.0523   4.048  1,   8      31 \xf8POWERSUPPLY TEST FAILED !!!\r\n

Eventually it starts repeating the messages "ERROR: No Valid Serial Number found !!!" and "ERROR: No Valid Hardware info found !!!".

2020 03 26 01:38:57.7429 0.001042  1,   8      22 BOOTLOADER PARSIVEL\r\n
2020 03 26 01:38:59.0512   1.308  1,   8       3 \r\n
2020 03 26 01:38:59.0522 0.001042  1,   8      21 *** PARSIVEL 2 ***\r\n
2020 03 26 01:38:59.0641 0.01184  1,   8      20 OTT HYDROMET GMBH\r\n
2020 03 26 01:38:59.0740 0.009899  1,   8      22 COPYRIGHT (C) 2019 \r\n
2020 03 26 01:38:59.0879 0.01393  1,   8      40 VERSION: \xf8POWERSUPPLY TEST FAILED !!!\r\n
2020-04-29,09:13:52|INFO|opening: s1_20200326_120000.dat
2020 03 26 19:49:41.7501 6.544e+04  1,   8      42 ERROR: No Valid Serial Number found !!!\r\n
2020 03 26 19:49:41.7597 0.009589  1,   8      43 ERROR: No Valid Hardware info found !!!\r\r\n
2020 03 26 19:49:58.6922   16.93  1,   8      22 BOOTLOADER PARSIVEL\r\n
2020 03 26 19:50:00.0337   1.341  1,   8      42 ERROR: No Valid Serial Number found !!!\r\n
2020 03 26 19:50:00.0577 0.02407  1,   8      43 ERROR: No Valid Hardware info found !!!\r\r\n

It keeps reporting the "No Valid Hardware info" messages until 2020-03-27,01:50, then some noise, then nothing until 20:13, when it starts reporting the default messages with the serial number of XXXXXXXX:

2020 03 27 01:50:38.3070 0.001042  1,   8      22 BOOTLOADER PARSIVEL\r\n
2020 03 27 01:50:39.0419  0.7349  1,   8      42 \x00\xe0\x00\x00\x00\x00\x00\xff\x00\x00\xfe\x00POWERSUPPLY TEST FAILED !!!\r\n
2020 03 27 01:50:42.5119    3.47  1,   8      33 \x00\x00\x00POWERSUPPLY TEST FAILED !!!\r\n
2020 03 27 01:50:44.8753   2.363  1,   8      44 \x00\x00\x00\x00\x00\x00\x00\x0e\x00\xff\x00\xfe\x00\x00POWERSUPPLY TEST FAILED !!!\r\n
2020 03 27 01:50:47.5648    2.69  1,   8      63 \x00\x00\xff\x02\x00\xfe\x00\xff\x00\x00\x00\x00\x9d(\x80\x00\xff\x00\xff\x00\xfd\xff\x00\x00\xfe\x00\xff\x00\x00\xff\xff\x00\x00POWERSUPPLY TEST FAILED !!!\r\n
2020 03 27 01:50:51.8081   4.243  1,   8      49 \x00\x00\x00\x00\x00@\x14\x00\x00\x00\xfe\x00\x00\x00\x0e\x00\x00\xff\x00POWERSUPPLY TEST FAILED !!!\r\n
2020-04-29,09:13:56|INFO|opening: s1_20200327_120000.dat
2020 03 27 20:13:06.5367       0  1,   8      71 XXXXXXXX;0000.000;0000.00;00;-9.999;20000;0000.00;025;27028;00000;0;\r\n
2020 03 27 20:14:06.5447       0  1,   8      71 XXXXXXXX;0000.000;0000.00;00;-9.999;19320;0000.00;025;27018;00000;0;\r\n

There are still some reboot messages later on and more error messages, so it's not like the disdrometer is stabilized again but just missing eeprom. Either way it's in a broken state, and I don't think this is the only one to have had this kind of problem.

For the moment, I have modified the NIDAS config to parse the messages but skip the serial number field. However, that is not a fix since the whole configuration of the data messages has been lost, and we don't know if losing the hardware info and any other eeprom settings makes the data useless.