@SandervG Yes it happened on 5 different pieces at the same height so yes, it's unlikely to be a pulley issue. All were printed with the 0.6 head and a carbon fibre filled nylon. And the glass plate was definitely secure.
I did another firmware update, switched the print heads to a 0.4 and did a test using the Tough PLA. This was successful and without any faults. Therefore I'm thinkning that there could have been an issue with either the filament, print head or both. I then had a timely update with Cura 4.11.0 and I've since printed without issues. Fingers crossed it continues but because I don't know the cause (fault with Cura 4.10.0 maybe??) if/when it does happen again, I prob won't know how to fix it.