Same here not sure if the Github issue is the same thing though.
Scanning logs from 2021-01-04 03:38:01 to 2021-01-11 03:38:01
2 Log lines scanned, 0 lines parsed in 0.12 seconds
Noticed after upgrading to 0.51 which I did early in 2021
Will check back through previous reports to see if I can pin down the change.
Edit: Confirmed that log was truncated when run on 2021-01-04 on MIAB version 0.48
Same again after upgrade to 0.51
Edit 2021-01-19
Noted that the oldest mail log on my server is from 2020 with all the later ones in 2021. Viewing the discussion on GitHub re this topic.