Steps to reproduce:
have some log files on monitoring with zabbix agent active with key

logrt[/tmp/log-a.txt,,,101,skip,,120.0,]
logrt[/tmp/log-b.txt,,,101,skip,,120.0,]

update the file regularly

• change time in the system back or forward (it could happen when the system is rebooted)

Result:

• agent re-read the files from begin every time despite on options and detecting the time changing and adjusting the mtime:

  26565:20200607:082950.670 the system time has been pushed back, adjusting active check schedule
   26565:20200607:082951.670 System clock has been set back in time. Setting agent mtime 46 seconds back.
   26565:20200607:072950.343 the system time has been pushed back, adjusting active check schedule
   26565:20200607:072951.344 System clock has been set back in time. Setting agent mtime 3675 seconds back.
  

Expected:
Do not re-read the file.