Premiere 14.1 Playhead lags when navigating timeline

Hi there.

Dealing with an annoying issue where the playhead intermittedly lags when doing general editing in the current Premiere 14.1.? on a 2017 imac.

It'll be playing down and I'll click somewhere else on timeline to play from (both with and without pausing playback first with space bar) and it'll continue to play the timeline for 2 or so seconds before jumping to where I placed the playhead.

It might do this every 5 edits, sometimes it might go 10 or so. Doesn't seem to relate to any projects, media type, or shots in particular.

I believe it maybe since updating to 14.0 which I did a while back but seems to be getting worse and slowing me down a lot on deadline.

The media is what I've used in the past with no issue such as AVCi HD off the Sony FS7 or ProRes.

I've done all the stuff I can think of inc...

Trashing prefs, updating Premiere to newest version, reverting layouts, clearing cache via Premiere and manually, changing GPU acceleration options from Metal to Open CL, updating Blackmagic driver for the IO. As mentioned it's across all projects, whether they're newly created in latest version or opened from previous. Reducing playback quality has no effect.

Machine is a 2017 imac retina 5k, 27". 4.2 i7, 24gb ram, Radeon Pro 580 8gb GPU.

Premiere is the newest version. IO is Blackmagic Ultrastudio 4k mini.

Media is on Promise Pegasus thunderbolt raids.

This setup hasn't changed for a while and has been reliable.

I do have OSX of High Sierra 10.13.4 which I do wonder about. I can't seem to find any other options to update the GPU firmware outside of the OSX path. However I am a little concerned about updating to Catalina when in middle of a TV series. I've heard plenty of disaster stories!

That said, I've got a month of intense editing to go and it's really painful not being able to...you know...edit properly!

Any advice hugely appreciated.

Cheers.

Cal