pert Funny you should say that about burning a bootloader, as that was what I did when my clone Unos seemed to play up after the IDE upgrade. There is a very useful 'Instructables' post on 'How to fix bad Chinese clones' which I used to cope with the CH340 problem when I first bought a clone. This time I did Uno to Uno as well as reinstalling CH340. Didn't realise I could do Uno to Nano. Fascinating!
Thanks too for the second part of your post. Really interesting.