Hi!
Although I don’t know the mod or the RTA, I think the phenomenon points to a contact error; that’s when the measured resistance of the RTA usually jumps and/or increases. Of course, in rare cases the mod might be faulty, but you wrote that it works fine with the Profile RDTA.
The contact error could be between the mod and RTA, or in the RTA deck; at least those two cases have occurred for me.
In the first case, the positive contact of the mod might be slightly shorter than average. Thus, if the 510 pin on the RTA doesn’t protrude much (it’s almost flush with the outer 510 threading), even if you screw it on properly, there won’t be proper contact. E.g., if you use a silicone pad between the RTA and the mod, try without it.
In the second case, the RTA’s 510 pin might not be tightened sufficiently, or there might be an issue with the wire/mesh clamping.
I am only guessing because your case is quite interesting.
Does it still show the correct value when you have put on the top part as well, when the RTA is completely assembled? I’m thinking something might shift while you screw on the barrel.
Is there a difference in how far the RTA 510 pin protrudes between a mesh build and a wire build?