Logs does not indicate anything special, in the timeframe that your log covers
When said, it looks like your PMS is outdated, and a version before 1.25.3.5385-f05b712b6
Please update ASAP, since we did put in some security improvements in 1.25.7.5604
See: Plex Media Server - #490 by Ridley
Also note, that I did a lookup on your account email address, and it shows at https://haveibeenpwned.com/
So if you shared password among different places, then that could explain it
