After quite a lot of searching around, I tried something that seems to solve the above issue.
I’m using a Child Theme, so I had to go into the functions in the Parent Theme: in the file includes/core.php on line 499 I added the following $text = excerpt_remove_blocks( $text );
This was added above this line: $text = strip_shortcodes( $text );
I’m not fully fluent in WordPress (or PHP), but is there a way of acheiving this by adding something to the Child Theme?