This isn't so much a bug in the game as it is an error in the Rise of Killbots levels' coding. For this reason, I wasn't sure that it would be appropriate to post this in Help and Bug Reports.

I noticed that both pistol and shotgun bullets in the Rise of Killbots levels simply weren't despawning despite having a BrickCleanup script, and the game would start to lag after enough shots were fired. It didn't help that the bullets curve upward for some reason. This curve basically allows the bullets to never hit the bottom of the map, which would otherwise delete them automatically without even needing a BrickCleanup script.

Then, as I looked through the game's assets and scripts, I discovered that the PaintballShooter scripts on both weapons were written to attach the BrickCleanup script to each bullet, yet they weren't written to enable it.

Tool.BrickCleanup:clone().Parent = missile

I fixed the problem by adding a line immediately below this to set Disabled to false.

Tool.BrickCleanup:clone().Parent = missile
missile.BrickCleanup.Disabled = false

Oddly enough, I also noticed the top comment on the BrickCleanup scripts saying, "this script removes its parent from the workspace after 120 seconds" when it actually takes only 15 seconds.

I noticed these issues on every Killbots map I played, so this isn't an isolated occurrence on one level. Since these levels are packaged with the game, I was hoping this fix could be brought into the game's next update, so other players won't need to fix these problems for themselves in the future.

i dont think much people care about that issue no offense

Most players probably won't care at first, but if they fire too many shots in a shooter game where the bullets don't despawn, the whole game will eventually lag out.

My main reason for posting this was to see if this problem will be fixed in the next update and, if not, offer a simple way for the players to do it themselves. Either way, my hope is that it can get fixed before too many people start to care about that issue, so it doesn't ruin their impression of the game.