Hi @BigBlue83, welcome to the forum 
Sorry to hear you’re having issues with your sonar reading consistency.
This thread may provide some insight, and this comment discusses DVLs but is quite relevant to reflective sonar technology more generally.
As a starting point I’d recommend trying to look at the profile data in Ping Viewer to see whether there are indications of how/why it is losing its distance estimate. If you have a known maximum depth of water then you may be able to avoid some of the drop-outs by disabling auto mode and setting a maximum scan range so it doesn’t try to search outside of that