Were you using DFS channels (52-144)? If so, I believe that DFS channels are not officially implemented in this router yet (the last time I read about this the mt76 driver did not have the capability to listen to radar signals with mt7613, so I believe that this might be the cause, but I am not certain about this).
It may be possible to use DFS channels if you select a country where these channels are not restricted. Notice that doing so if you are not in the selected country may be against the law.