Browser struggling & very slow which clicking between blocks

We have a post that has just over 20 content blocks on - nothing complicated to them, just some general content layouts, images, a couple of repeater fields and that's all.

When we initially go into edit the post, it takes a few seconds to load them which is to be expected. The issue we are having however, is when clicking between the different blocks after the page has loaded.

Firstly, if all the blocks are toggled to 'Preview' mode then there is no issue and it pretty much instantly switches between blocks. However the more blocks we have toggled the 'Edit' mode, the more it seems to slow down dramatically when you then click between the blocks and can be 5-10+ seconds after you click the block before it becomes active/selected.

I can see that an AJAX request is made when clicking between blocks, however that long load time is takes place before the AJAX request shows in the network tab. For example: Click on a different block, browser gets stuck for multiple seconds (can't click anything else during this time), then the AJAX request fires (only takes around 1 second which seems normal), and then then the block is selected and you can carry on editing.

We've tried:

• Different browsers in case any extensions interfering - issue persists
• Disabling plugins to ensure there is no conflict - issue persists
• Removed the markup from the blocks in case there was a performance issue there - issue persists
• Deleted the corresponding ACF group for the blocks - issue goes away

The big one to note here is that if I click the Gutenberg 'Settings' cog to close the right sidebar, the issue goes away completely. That would suggest it's something related to the loading of the ACF fields with slightly larger posts?

Happy to provide you with a login to a staging site or a video which may help explain things better than I have here!