Hey folks, has anyone run into this problem before?

Got two RBI racks running on a Herpstat 2, backed up on Hydrofarm t-stat. Probes correctly placed on heat tape, secured with electrical tape. Herpstat 2 says the temps are in low 90s as set, but temp gun reads 75-80 on warm side of tubs over heat tape where probes are set, and only a degree or two higher on the tape itself when tub is removed from rack.

I believe the temp gun b/c snakes feel cool to touch and temp gun reads appropriate surface temps on the other sides of the tub/other surfaces in rooms.

Any ideas? It seems to me the problem must be with the HS2 or the probes as opposed to the rack. The only recent change is that I used to use the HS2 on one rack and two freestanding tubs, and recently switched out the tubs to another t-stat and put the second rack on the HS2.

Thanks for your collective wisdom!