Fixing Z-Hop Stringing
Stringing may depend on sub-optimal retraction settings: when retraction is fast and high enough, the string may be cut and disappear.
You may want to at least try to optimise retraction, at least to exclude that parameter.
There is a tool designed to properly tune retraction:
http://retractioncalibration.com/
What it does is print a tower with multiple retractions with increasing retraction distance around the perimeter. Along the Z axis the retraction speed is increased.
This tool does not include Z-hopping so stringing may be less visible, but at least you can easily visualise the optimal retraction settings. At that point if the optimal settings are much different from what you had, you may want to try your model again to see if it improved.