There are two GNS530 mods since SU11. No big issue with the older PMS50 one. But the new WT GNS530W mod that can be installed from the marketplace creates problems for the GTN750. Did you install this from marketplace? (Does not appear in Community).
PMS50 has published a mod to fix this. You might check here - WT GNS530 Compatibility
The issues are in the core AP changes which is loaded by the WT GNS530W even if the GNS750 is chosen by tablet.
Curious - you can post here -
Aircraft that are designed to choose GPS by livery (example Flysimware 414AW) have fewer issues. The WT mod is not fully compatible with aircraft that choose GPS by tablet or hot-swap (example Milviz C310R)