OK, so I checked my SD card and confirmed that all my sensors ( I have quite a collection) are being logged and so I suggest that you might not be running the latest firmware.
Firmware update sort of addresses the issue, but not fully. I was on V1.6.0 instead of V1.6.7. The behaviour is still quite strange:
1. "Backup-_" files do not included the additional sensors (Underscore is replaced with the actual alphabetical serial #). These large files are the only ones that contain the longer data logs.
2. "202010A" file does include the PM2.5 sensor but not the other sensors.
3. "202010Sensor-A" contains the soil moisture sensors, PM2.5, and water leak sensor data only (and provisions for other sensors).
4. "2020SM1A" file that only contains the CH1 soil moisture readings which is redundant to "202010Sensor-X" .
5. "2020CH1A" file contains channel 1 temperature and humidity sensor readings, which are not included in "Backup-X"
6. "2020CH2A" file contains channel 1 temperature and humidity sensor readings, which are not included in "Backup-X" nor "202010A".nor "202010A".
7. All of the "2020...A" are continuously modified and not tied to the 'manual backup' function which is run on the HP2553BC unit itself through settings menu. It looks like they store data from when I first installed the unit (until they are deleted then fresh ones are made). Not sure if there is a limit to how much data these files will store.
8. It would make more sense that these files are all merged into one, but probably these files have been added in incremental firmware updates (a sort of bloat/maintaining prior files).
Other added notes:1. WS View displays HP2553BC Wifi EasyWeather Firmware only (V1.5.4), not the main firmware (Pro_V1.6.0 / V1.6.7).
2. To view the main firmware, on the unit itself it is shown in Settings, About Display.
3. To update the main firmware, the Ecowitt website says "
2. Drag the unzipped file under the root directory of your microSD card." This is not exactly accurate because you need to copy "user.bin" over and not the whole "HP2551_V1.6.7" folder which it is zipped as. I suspected this was going to be an issue and it was just a minor annoyance of the instructions, mostly because microSD removal and insertion must be done carefully.