Unplayable FPS drops - which can be fixed by returning to a 'communal' area???

Since the last patch I've had an issue which makes the game pretty-much unplayable.

In ANY sort of map or even in my Hideout I will regularly see a massive reduction in FPS - the game becomes a slideshow tho i can still move/interact/fight.

If I teleport to a communal area (e.g. Ziggurat Base) it fixes itself - I can then return to my Hideout or directly into the Map and everything is fine again!?

If it gets REALLY bad, I can't even teleport because the game says "You cannot do this when the game is paused" - except it isn't paused - combat etc. continues?

On one occasion it started as I engaged a boss - managed to complete the boss but the loot took OVER A MINUTE to drop

Next time that happened NO LOOT DROPPED AT ALL - nothing (disabled filters) and the boss (Lort of Dirt? Uses green balls which fire spikes) kept spawning forever???

Note: this can happen even if I'm sitting my hideout doing nothing which rules-out a LOT of possible causes...

No unusual CPU or GPU activity, no ecessive memory usage, ping is normal - frame graph has massive 'white' spikes - I'm pretty sure it's not me...

Ideas?

p.s. Vulkan all defaults on AMD CPU/nVidia GPU if that's relevant - latest drivers and all that jazz