I have updated two RB750UP ros 6.43.2, when I try to update the firmware the RB stops working and needs a full reset.
The current firmware on board in 3.19, I would like to upgrade it to 6.43.2 
I tried a search on the forum but I did not find any information.
I add:
at every reboot I have to completely reset… it is not normal!!!
Hello, I have same problem with upgrade firmware on 750UP (i have 30 routers). I try to send this problem in Support with [Ticket#2018100822005227], but they recommend to use NetInstall. It’s not working for me. I noticed that after upgrade firmware eth led began fast-fast blinking.
same here 2 rb750up
we had to netinstall them with 6.42.9, no more tries with 6.43.xx for a while for us
I have similar problem. but with RB751u-2hnd. this RB is previously hacked with coinhive-virus.
http://forum.mikrotik.com/t/rb751u-hacked-now-cannot-upgrade-using-netinstall/124444/1
I can update 750UP to 6.42.10 firmware with disabled poe and firewall.
We have detected these problem with more than 5 RB750UP. When we try to upgrade firmware then it not starts.