mdf:
The way I read the OP was that following a reset the wifi works fine. After a period it will stop, then after a reset it will work fine again for a while.
I would have thought that this would point to a fault, not interference? I might have read it wrong though.
What firmware are you on?
To me, it points to a memory leak.....and the router is doing a job with a bit of memory...a bit more memory...a bit more memory (not freeing enough to be sustainable) and eventually whatever table / resource it's using can't get any more memory......and it just fails - partially or completely (memory leaks can be like that). It also gets slower before failing. Seen that.
A reset clears the memory and you're good to go until it fills up again.