I'd start with the basics,
Clean everything.
Ensure everything is Torqued to the correct specifications
Ensure Scope is mounted correctly
Clamp/secure gun in mount
Put 5 rounds with same aim point.
If the group is not acceptable, remove moderator, check for clipping
Put 5 rounds same aim point different than above without moderator
If group "magically" tightens up, the mod is suspect.
Continue to fire rounds as the barrel may need to be "leaded" before groups tighten up.
Try different pellets until a consistent group is established, then tune for pellet to tight up group further.
My Brocock Bantam MK1 .25 cal (unregulated) was pellet on pellet at 25 yards and 0.5" at 50 yards. That is until it took a header off the table. Then it went to 6" group. I checked the moderator and it had bent the inner steel disk. Tried a buddies Tonto, which is shorter, and we are back to close to what it was, but something is still "OFF". I've sent it back to AoA for checks and any repairs needed.
Smitty
PS - Free advice is only worth what you pay for it.