Quick answer: Modded installs produce bug reports that aren't real bugs. Detection and tagging of mod environments separates moddable from base-game issues.
Mods are a feature. Mod-induced bugs aren't your bugs to fix; they need to be distinguishable.
Detect mod env
SDK checks mod-folder existence and content checksum at startup; flags in bug reports.
Tag at submission
Bug reports include 'mod environment: yes/no/list'. Triage filters.
Reproduce in vanilla
Mod-tagged bugs: reproducer tests in vanilla first. If reproduced: real bug. If not: mod-induced.
Communicate transparently
'This bug appears only with mods enabled. We can't fix; suggest contacting the mod author.'
“Modded environments are common. Detection is the basis for triage.”
If your game supports mods, plan the moddability detection in the SDK. Reports without it can't be triaged efficiently.