Waste heat problem?

UPDATE: The box was obviously defective. The spare box works perfectly and meets nearly all expectations that I had.
The only thing I'm missing is a way to tunnel all Internet traffic through a freely selectable VPN. That's too bad.

I got out of my o2 Fritz! Box yesterday and after the initial euphoria I have the great DSL sync bug. After about one hour of operation the box the DSL Sync loses every 30 second intervals.

I've tried everything that was caught in the relevant forums and by AVM: Cable traded, checked phone socket, changed the place of installation, another outlet, all other devices switched off. Nothing helped. The only thing that struck me was the fact that the box after longer breaks without electricity worked uncomplainingly for 20-30min repeatedly.

To verify that I have brought the box then run until the sync problem occurred again and just put a cold pack from the freezer compartment underneath without removing the box from the mains and then they walked on immediately with no problems. After removing the cooling pack the sync problem came after about 2.5 hours.

Since it seems well to give massive Qualtitätstreuungen, or the board layout is not favorable, whatever, I hope the Ausstausch box does not have the problem.

For the price in any case an imposition.