GT-AC5300 Firmware Version 3.0.0.4.384.81695 and USB 3.0 HDD
The update was done again and everything was set again.
After restarting for hours everything is OK but later the processor starts to go crazy, one core 100% and every now and again another has 100% and the other 3%, memory 97% occupied, on my previous RT-AC68U there were no such situations.
Of course, nobody from the network uses the processor at the time.
When you anticipate any updates, the RT-AC68U has updates every month or two and everything went well there but it is too weak for my needs.