I'm having this problem on a piece I'm writing but I cannot reproduce it by extracting the single measure.
So no minimal example, I'll just attach the image showing the problem: the slur between two notes is moved up because of a right-hand fingering on the first one.
This is the relevant line:
<ees\5-\rightHandFinger #2 >8( \glissando e4\5)
I've read NR 4.4.3, Vertical collision avoidance, and tried few overrides using outside-staff-priority and avoid-slur, but honestly I don't know really what I'm doing.