Problems with TP-Link routers working as repeaters

I purchased two old TP-Link routers, TD-W8970 and TL-WDR4300.
So, I have the net in the image below.
Both routers have Openwrt installed and are configured as repeaters.
Whether I connect them to the Afoundry EW750 or the other main router, the repeaters work fine for a while (it can be a few hours or two days), but then the Internet starts to freeze.
One of the two TP-Link routers now configured as repeaters, as far as I remember, also did it with the original firmware.
Now, I don't understand what's going on.
What's the problem?
I thought about planned obsolescence, that is really sad.

You haven't given many details about how you achieved the configuration -- we don't even know what version of OpenWrt you're running., but a few thoughts:

  1. These devices were never designed to be repeaters. If you're using relayd, it is a bit of a hack (but it is a necessary method in many cases)... so if it's not the best expereince, it's not suprising.

  2. I think these devices have only a single 2.4G radio (although I may be mistaken)... this means that the performance will be cut in half to begin with.

  3. You're using a non-standard channel for the EW750 -- I'd recommend using 1 or 6.

  4. If you can run wires, that will make a huge difference.

And on this:

You're using old devices. OpenWrt gives them a second life and extends the usefulness of them for a long time relative to the vendor's support horizon. However, technology marches on... it's not about planned obselence, but rather the progression of technology... you're on 802.11n devices and we've now moved to 802.11ac and 802.11ax as the predominant standards -- improving speed and performance and an overall better experience for users.

There is no such thing as WiFI repeater in the 802.11 standard. You didn't specify if you used relayd or another solution.