FCPx Memory issues - Crash

I am having serious problems with FCPx 10.4 for a week, with memory crashes caused by both Importing and/or Rendering.

I am importing/rendering to external drives, yet FCPx gobbles up all my 30Gb space on my internal drive when importing or rendering, and also does same for RAM memory, within a minute or so of starting the process, bringing my computer to a crash.

The program is unusable at present, and causing havoc.

(In fact after my last crash, even my Mail accounts were all missing. Thankfully on a subsequent reboot they appeared again.)

I have tried trashing preferences, but to no avail.

Regards,

Geoff