Heavy RAM usage and freezes when trying to download an attachment

Hi all

I have just started using Mailspring and really like it - I have just upgraded to the Pro version.
However I keep getting notifications that it is using heaps of RAM & also when I try and download an attachment by clicking on the down arrow, it just freezes and I have to force quit and reopen it.

I want to keep using it as I really like the feel of it - but I need to get these issues sorted obviously!

Any help greatly appreciated.