Strong 1200 (a.k.a. MTC WR1201), Ethernet disconnects frequently

Hello,

I experience very frequent disconnects of Ethernet link on Strong 1200. Up to 9 disconnects in a half an hour. Strangely, the frequency of disconnects increase from 08:00 to 12:00 and decrease from 12:00 to 18:00. Each disconnect lasts for 10-25 seconds.

This problem emerged when I used OpenWrt 19.07.7 r11306-c4a6851c72. I have tried to upgrade to the latest snapshot, but nothing changed.

Other strange thing is that most of disconnects occur on a connection with ISP. When I plug the cable from ISP into other devices, there are no such disconnects. I have tried to reconfigure switch in the Strong 1200 router to plug the ISP cable into another port, but it did not change anything - the disconnects still occur.

There are also a few (1-2 per day) disconnects on Ethernet connections between this router and other devices.

What I am trying to figure out here is whether the problem is in the firmware, or is it just my device is broken. Does anyone have the same problem with this device?

@vk496, do you know, is it safe to try to flash stock firmware from here? I want to test how it would work with the stock firmware. That two-stage OpenWrt flashing process required for this router raises some questions and worries. One of them is that it seems like the original firmware assumed, that the partition with its configs would not be overwritten during firmware upgrade.

But at least binwalk tells me that the stock firmware image contains uImage header, similar to ones in OpenWrt firmware images.