Hello Dom,
The callstack looks to be similar to the one in this post:
https://forums.unrealengine.com/t/help-crashes-assertation-failed-uniform-buffer-etc/2140967/40
I believe your 5.5 version is 5.5.3? Can you try upgrading to the last hotfix? 5.5.4?
Or, if you are building from source, this is the changelist that should fix the crash:
https://github.com/EpicGames/UnrealEngine/commit/bee3551cc2942b82482f2023226b60fc2b0fb9f6