Forge: forge-1.12.2-14.23.5.2847-universal
Mod Version: randompatches-1.12.2-1.21.0.3
Mods List: RandomPatches (only)
latest.log: https://gist.github.com/pinkpig3777/d668ca627c9691fc7d1fc7dc0e538ad4
debug.log: https://gist.github.com/pinkpig3777/cf97fbc8a8918aa1ad94cfd77cf98431
Warning Message:
[10:36:37] [main/WARN] [FML]: The coremod com.therandomlabs.randompatches.core.RPCore does not have a MCVersion annotation, it may cause issues with this version of Minecraft

I noticed this issue post has the same line in it. Thus I tried the solutions you offered one at a time:
Setting B:patchMinecraftClass=false did not fix the issue.
Re-enabling that option and setting patchTitleScreenOnDisconnect=false did not fix the issue.

Thus I've re-enabled both.

Additionally, on CatServer it shows this error (which starts with the SAME warning message):
https://gist.github.com/pinkpig3777/09266604711fcf1184ac902bbcbb8cf5
CatServer's latest.log: https://gist.github.com/pinkpig3777/8ae9dedbf6d47fc18b1299481cf6c373
CatServer's debug.log: https://gist.github.com/pinkpig3777/a89b2ab81543a604a237af20a9673581

How can this issue be fixed? I mainly use CatServer but compare any errors to normal Forge when I report issues. And both show the same warning message but CatServer gives additional errors afterwards.

Help would be greatly appreciated, thank you!

RandomPatches intentionally does not have an MCVersion annotation, as it does not allow the specification of multiple versions. The 1.12.2 version of RandomPatches is written to work on all Forge versions from 1.8 to 1.12.2, and an MCVersion annotation would prevent this. The message can safely be ignored.

Oh, and the second error can be fixed by disabling misc.portalBucketReplacementFix. It's probably a conflict with Spigot.

Oh, and the second error can be fixed by disabling misc.portalBucketReplacementFix. It's probably a conflict with Spigot.

I believe that fixed it. Thank you!