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This is A1200 from Escom or Commodore? Because as with Escom, there are problems with the floppy disk drive, the same may apply to the second A1200. Only it would be a bit strange that Wicher somehow fixes it.

This may indicate that the CHIP memory is corrupted somewhere within the higher addresses.

I thought about it too, but the problem occurs on a few Amiga's (in fact, a third was tested).
Unless it is an old age affliction of each copy, which is hidden with an expansion card

I cannot answer this question. The plate in revision 1D4.
Fully wired floppy drives were also tested on other drives.

I hope, at least it would be a bad luck to the max.

During the purchase, WB was fired plus some game.
I briefly checked the joystick, mouse, keyboard, graphics and sound.
Everything was OK.

The seller recorded a Lotus 3 for me. I returned with the Amiga, in two days I received SWOS and WB 3.x Cloanto, purchased elsewhere, and none of the three floppy disks is included.
Well, maybe I exaggerated, Installer Cloanto starts without problems. This bootable throws disk error

The disks may be damaged as they were burned without verification. Run x-copy and give Check. Everything should be green. The memory may also be corrupted, but it probably wouldn't be in a couple of Amiga's at once. Or maybe you run a virus on startup.

Do you also have Kicstart from Cloanto? Have you checked your disk for viruses?

In the case of games, it is rather standard that there may be problems with those written for older models, sometimes disabling the processor cache and switching the chipset to the original (I think) in the bootmenu, or the so-called ks1.3 emulators.

Yes, kickstart from Cloanto too. I do not have the disk, I have not checked the floppy disks.

It seems that these Escoms have a joy port on the ribbon and not on the motherboard. And they needed a fix to boot non-random floppies.

I checked those X-Copy disks.
Both SWOS and System (Bootable) Cloanto report 6-files in some sectors of the floppy disk.
Lotus looks okay, but won't boot up anyway.

It remains a mystery why the extension helped then, and why the problem occurred on several Amiga. Tomorrow I will have my own (Wicher 1211) and let me know.