Antenna Tuner Inconsistency Question

Hey Reddit...My MFJ-949 tuner that used to tune my dipole to 1:1 SWR now only tunes it to 1:1.5 SWR. I opened the case to check for arching, but with the case top removed, it is back to 1:1 SWR. Adding the top at the exact same L and C settings, SWR is back to 1:1.5. My only guess would be that the case is interfering with the inductor's magnetic field, but I do not know what caused this to spontaneously change. There are no apparent shorts between the case and the components. I was wondering if anybody else has had experience with this issue? I appreciate any help.