I've put OpenWRT on the Flint 2, and I've had issues with connectivity that I don't have with OpenWRT on a Linksys router. I need to disconnect and reconnect every so often. I'd read that this is due to the Mediatek modem not being as well supported, but I'm not sure how to diagnose.
Have the same router (Flint 2), and had a similar issue in the past. After I configured SSIDs with different names on the radios (i.e. the SSID is either configured on radio0 or radio1, not both), I didn't encounter this anymore. YMMV, but this helped me - perhaps it'll prove useful to you as well.
And besides this issue, overall it works great. I recommend this to anyone who asks me about it.