Again, thank you, but again, i never ever used isolcpus in my life, yet i have over 30 machines running LinuxCNC and Mesa hardware happily, every day, on mostly industrial machines, for over 10 years.
Still, i understand that sometimes isolcpus and some other tuning can help.
P.S. that 30 above does not include over 15 PC's and laptops i own, all with LinuxCNC and used on machines with Mesa boards, and therein lies my dilemma, i have plenty of laptops that run LinuxCNC out of the box, but i can not advise on getting the same laptops as i had two of the same make and model where one was OK and the other was utterly useless. And i use USB-to-LAN adapters and switches, but i never ever advise others to do the same thing, as i am fully aware of the consequences, if something fails.

I did not say to switch slots, although that might help on old PC's or if the memory pins were touched during installation, i said to test each module, one at a time, and that is still valid advice, had new 16GB module fail inside a week lately, out of 6 modules one failed, and the PC will boot with it and work till starting new apps does not work anymore and the PC reboots on it's own.
Sent it back for replacement, got it back with the note "it works fine", now i have to call tomorrow (well today as it is 5:15AM here) and explain to them that booting windows does not work as a memory test.
I did test it, on 4 motherboards, on 3 it works and memory test fails miserably, on one board it will not boot at all, even after BIOS reset and XMP/EXPO disabled.
The other things that might cause such issues, power supply (hard to check without replacing, needs a scope), and in your case might also be the motherboard as A520 are the low tier for AMD, so signal integrity for the memory controller might be compromised, although AMD is pretty damn good at fixing errors.
But first, disable XMP/EXPO in BIOS and test.

I am glad as i ran out of options a long time ago as most of it did not make sense!
What Asus?
If it has two or more sticks of RAM, yank one out and test, then yank the other and insert the first one, test again.

Rod, this would have been much more useful in the "driver boards" or EtherCAT or both sections, not here as OP has actual networking disconnecting, same as physically removing the cable.
I really appreciate you trying to help, but i really do not like when you point members of this forum and whoever reads this in the wrong direction.
This is the second time i am mentioning on this topic that none of that tuning will help with a disconnected link.