I've previously had my A2's mining at Nicehash with no problems other than a slightly lower reported hashrate on the pool end. Didn't have any issues with switchovers though.
Where are your A2's from, maybe the firmware needs upgrading?
I have had no issue as well, when I mined it a few weeks ago. Now it switches so often that the hash rate is reduced dramatically. Nothing wrong with the machine. I think it is just not acting well with nice hash because they require specific fixes in the mining software to operate correctly. I see where I can download an image of the software needed for the miner, but I don't see where there are updated versions that have the fixes nice hash needs.