audio waveforms disappearing and reappearing

I just converted a project from a Premiere timeline to DR, then created Optimized Media in ProRes LT
Original footage is all H.264 in UHD and Premiere just cannot do it.
My timeline converted fine but after editing for a bit of time my audio waveforms started disappearing and reappearing. Most of them will be there, visible and audible. Then I go further down the timeline, and clips from the same camera have lost their waveforms - they are no longer visible or audible. Then I go further down and there are waveforms on other clips. If I open the clips w/o waveforms in the source window and play them, the waveforms appear in the source window and I can hear the audio. But not in the timeline.
I've restarted DR a couple of times and the waveforms have reappeared in some clips. Also restarted the entire system and others reappeared. But not all! So seems like an issue related to cacheing or linking to the optimized media files. Or is the computer bugging out? Its on the older side but has been doing great with DR so far.
Is this a memory issue? One one file I waited and keep clicking and then the waveforms finally reappeared. But the computer is not acting like it usually does when the memory is maxed out. Playback is mostly fine, nothing else lags, other programs run well.
All the media and cache files are on the RAID drive, in different directories - could that be the issue? Should the cache be on the computers hard drive?
Or is this the graphics card or processor?
Starting the software over and over will clearly not cut it so wondering how to actually fix this. This is a 15 minute doc short, the longest I've tried to edit on DR. Is a test as to whether I should try to do a feature, and if this is what happens 8 minutes into a timeline then DR is failing the test!
Running DR 14.2.0
Mac OS Sierra 10.12.6
Retina 5k
3.3 Ghz
8GB DDR3 memory
MS Eswon R9M395
Original footage is all H.264 in UHD and Premiere just cannot do it.
My timeline converted fine but after editing for a bit of time my audio waveforms started disappearing and reappearing. Most of them will be there, visible and audible. Then I go further down the timeline, and clips from the same camera have lost their waveforms - they are no longer visible or audible. Then I go further down and there are waveforms on other clips. If I open the clips w/o waveforms in the source window and play them, the waveforms appear in the source window and I can hear the audio. But not in the timeline.
I've restarted DR a couple of times and the waveforms have reappeared in some clips. Also restarted the entire system and others reappeared. But not all! So seems like an issue related to cacheing or linking to the optimized media files. Or is the computer bugging out? Its on the older side but has been doing great with DR so far.
Is this a memory issue? One one file I waited and keep clicking and then the waveforms finally reappeared. But the computer is not acting like it usually does when the memory is maxed out. Playback is mostly fine, nothing else lags, other programs run well.
All the media and cache files are on the RAID drive, in different directories - could that be the issue? Should the cache be on the computers hard drive?
Or is this the graphics card or processor?
Starting the software over and over will clearly not cut it so wondering how to actually fix this. This is a 15 minute doc short, the longest I've tried to edit on DR. Is a test as to whether I should try to do a feature, and if this is what happens 8 minutes into a timeline then DR is failing the test!
Running DR 14.2.0
Mac OS Sierra 10.12.6
Retina 5k
3.3 Ghz
8GB DDR3 memory
MS Eswon R9M395