Text editing is sometimes slow when using cursor keys

I’ve recently noticed that sometimes if I use the cursor keys to navigate around a section of text it can take a second or two to catch up on the number of cursor keystrokes, and then my edit will be inserted/deleted in the wrong place. It can be a simple text-only two or three line message, no images or links. More complex posts seem to be about the same. Left arrow is worst.

This only happens with this forum, none of the embedded editors in other websites I visit are noticeably slow.
It seems to me that this somewhat random slow down is recent, perhaps just a few weeks.

The only significance I’ve noticed (red herring?) is that it is more likely to happen in a popular topic with a lot of posts or when editing a previous post, but even this first post in a new topic has begun to suffer as I have tidied it up and tried to make it clearer.

Sometimes (less often) when it is slow I can also beat the screen when simply typing, at first I thought it was just me missing keys but a test running a repeated pattern on an edit showed it.

Machine is a Dell E6540 CORE i5 with 8GB RAM, 500GB SSD, W7P using just one tab on latest FF 83.0 and a proper AT102W keyboard plugged into the docking station.

I just checked the Task Manager, 5% cpu in use, mostly FF and Norton.

Get the same with my phone key pad, it’ll freeze too. Sometimes the text will jump or even be missing. Ok this can happen on other forums but worse on the OC site.
I’ve just reformatted two laptops and now working on Linux, getting there with them but I’m having problems the same with typing text on the OC site, sounds much the same as yours.
My phone BTW has done an update and since then the key pad can freeze whilst typing, so too my wife’s, hers was ok until she had the update, same phone, Motorola.