Preview consistently unstable on fullscreen

Hi all,

I've recently been having real stability problems with Preview when viewing pdf documents in Preview (mainly text) on Macbook Pro OSX 10.13.3 (Early 2015 - 8GB Ram, 2.9GHz).

Tends to emerge when I have a few documents open in different tabs in split view and then change the reading view (i.e. single page to continuous scroll) - though its arisen spontaneously too. The toolbar then suddenly disappears, and all functionality (copy, highlight, add stickie etc) goes apart from scrolling through the text and highlighting.

Because the toolbar no longer appears, and cmd+Q doesn't work, I force quit and restart and the problem then re-emerges within about 15mins.

I've tried multiple reboots, all different kinds of document, tried running alongside no other apps, or incrementally alongside typical work apps (Safari, Mail, Word) but hasn't gone away.

Any tips would be much appreciated as it really gets in the way of workflow!

Many thanks in advance