Using only one methodology (OFX or MD+) is the correct way to go.
If you have both active, disable one and go from there.
That said, for me personally, I prefer OFX to MD+, so, for example, I use OFX (with the OFX fix) for USAA, and MD+ for Schwab (as Schwab no longer supports OFX for non-aggregators.) To put it differently, for me, OFX if OFX works, MD+ if not.
You can decide either way - just disable the one you do not want.
If that doesn't work, launch toolbox extension, enable update mode, online banking tools menu, Delete OFX Banking Service and select the OFX profiles to delete.... Might be a good idea to run the Cleanup Banking Links option too...