Thanks. I'm leaving it within UNII-1 range for now, to see if it is stable there. It is congested but not impairing performance really.
The thing with DFS is, I live within 5 kilometers (3.5 miles) from an airport which has both civilian and military use. The radars will always keep knocking...
I just learned 52-64 was also DFS range, thought it was only 100 and above. Makes sense now and understandable why it takes a minute to clear.
Please disregard my original post, apologies for the confusion.
My RT-AC87U keeps auto-changing 5GHz channels despite control channel being set firmly to 52. Sometimes it stays on for long hours but just in the last two hours it moved to 48 and 40, then got back to 52. I'm not even using DFS channels, it would have been understandable to get knocked off...