Problem: This is seemingly a long-standing bug with the patrolled/unpatrolled revisions that occurs when a user with autopatrol user right (i.e., autopatrolled users and administrators) loses that status. Their previously automatically patrolled, and possibly their manually patrolled revisions prior to them gaining that status (sorry, can't remember exactly on this point), become unpatrolled.
What should happen: The previously automatically patrolled, or manually patrolled, revisions, should remain as patrolled, consistent with what occurs on the Wikimedia-owned wikis.
Reproducable? Yes, I have verified this on the revisions of User:Melan, User:Examknow, User:Covid-19, User:Artix Kreiger, et al., on Public Test Wiki (one example is at these revisions), which @RhinosF1 has now verified independently. Also reproducable on any wiki, really, including Meta, Commons, and more
Vivaldi 3.1.1929.45 (Stable channel) (64-bit)
OS Windows 10 OS Version 1909 (Build 18363.959)
Flash 184.108.40.2067 C:\WINDOWS\system32\Macromed\Flash\pepflashplayer64_32_0_0_387.dll
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.119 Safari/537.36
Command Line "C:\Users\Wylie\AppData\Local\Vivaldi\Application\vivaldi.exe" --flag-switches-begin --flag-switches-end --enable-audio-service-sandbox --ppapi-flash-path="C:\WINDOWS\system32\Macromed\Flash\pepflashplayer64_32_0_0_387.dll" --save-page-as-mhtml
Executable Path C:\Users\Wylie\AppData\Local\Vivaldi\Application\vivaldi.exe
Profile Path C:\Users\Wylie\AppData\Local\Vivaldi\User Data\Default