Does the cleaner turn up around midday by any chance?
IT joke aside, is something being turned on daily at that time that could somehow interfere with it?
Its a shame you can't arrange for the technician to turn up at that time.
Years ago I had a problem where if my telephone rang, my internet died. Engineer turned up and said it was impossible so I started a constant ping going and called my number from a mobile and he watched the pings stop responding. Turns out some bad cabling near/under the street had got wet and the increased voltage or something of the incoming call affected it. Would never have got that resolved without him seeing it.