OK, so I too had this problem. I took a look at the logs on my OSPi and found a few strange entries across the last 6 months of files:
[254,4,120,1485693673, inf]
[99,4,120,1485696549, inf]
[99,4,120,1485697194, inf]
[99,4,120,1485698351, inf]
[4,4,108,1486404109, inf]
[4,4,117,1487008918, inf]
If you have a flow meter enabled then the final field should be the flow rate associated with the station run. I think the “inf” could be the result of a divide by zero error and the log entries are rejected by the App and trigger the UI error message. Removing these lines resulted in successful logs being displayed for me in the UI. Looking at the code, this could happen if you have a Flow Meter enabled and short duration/low flow runs (my station 4 is just a single dripper for < 2 minutes).
I would be interested to know if this is the same issue as mentioned above and in #46873. To check, on OSPi, you can login to the Pi, change into the log directory and type “grep inf *” to see if any of your logs have this. On OS (and OSPi), you can use the web api to download all of the logs by typing “http://os_ip:8080/jl?hist=300” into a web-browser (may need MD5 password hash if enabled) and take a look. You can then delete just the individual daily files rather than the entire log history. Let me know.