PR2000 as extender stops listing my network out of the blue

I use NETGEAR Trek N300 Travel Router (Model: PR2000) in wireless range extender mode. Most of the time it works fine, but out of the blue it stops working (usually for a couple of days, but sometimes for over a week) even though I can connect to and navigate normally from the base router and signal diagnostics look normal. After an unknown, seemingly random amount of time it starts working again without any apparent reason.

When the extender is out, my network does not appear in the list of extendable networks at NETGEAR Genie (again, even though I can connect to the base router with multiple devices and navigate normally). The Power and Wifi lights are one, the Internet one is not. Restarting the router does not solve the issue - sitting tight and waiting has done the trick so far, but it's a nuissance not to be able to access wifi everywhere in my house when I have an extender.

Because every time the extender behaves like this my ChromeCast (which connects to my base router, not the extender) stops working as well (message states it is connected to my network but cannot access the internet - even though I can access through laptop, smartphone and tablet), I'm pretty sure this is a problem with either my internet provider or my router rather than with the extender. However, as is usually the case, my internet support has not been very forthcomming in finding a solution, usually arguing the problem in on premisse rather than on their end.

I would appreciate is any ideas on what could be causing NETGEAR Trek N300 (and ChromeCast) to behave this way, so that I can have an informed conversation with my internet provider.

Thanks in advance!