TP-Link WiFi extender not seen by GL-MT1300

I have a GL-MT1300 working in router mode.
When I bought it, few months ago, I connected it to a TP-Link WiFi extender (AC1750). It was working until yesterday, when I realized the extender is not visible by the router any more (using the scan feature the extender was not found, only if I reset the extender is gets visible but when the extender is configured it gets list again). After a small research I realized that this extender has got an auto mode that allows it to change channel (on both 2.4G and 5G bands) to ensure better wireless performance. So now it is on 104 channel. That channel is not configurable on GL-MT1300 and I believe this is the reason why the WiFi is invisible to GL-MT1300.
Firmware is 3.201 (upgraded on 2/4/2021).

Any solution to the issue?

I faced the same issues and honestly I was wondering why only so few people were bothered by it. The problem is that the driver support for the MediaTek 7621/7615 chipset is bad in FW 3.201 (as you can see from the fact that LuCi does not work properly), the country settings are not appropriate (and, even worse, not configurable via GUI) and that DFS is obviously not working. See my other post for a workaround. MT1300 (Beryl), FW 3.201 and DFS. I am still thinking about returning my Beryl and getting the slate.

It is about DFS. Maybe just fix or limit channels on your extender

My extender does not have any such option