KHD ph probe question

I recalibrated my ph probe and for whatever reason, when I reinstalled it, a leak started b/w probe and nut. I lubed it and it helped and now just getting a drop or two but now while observing for leaks, I noticed the probe backout about halfway and no leakage. I tried to insert and noticed that there was pressure causing it to back out. Towards the end of the cycle the probe settled in but not all the way. The vent tube behind the KHD is not kinked. Anyone have any idea on cause?

Perhaps the internal vent tube is clogged which is preventing air from actually escaping from the VENT.
You can verify this by opening the KHD and seeing if there is a small in-line filter blocking the vent. Remove this filter and reassemble.