Client side unstable in beta 3 rc2

We’d been experiencing some issues recently with alot of our 900 Mhz clients haing poor signal quality and being very unstable. Yesterday, we upgraded the 900 Mhz AP on the tower to Beta 3 rc2 and added 2 clients to the AP by upgrading their CPE as well. Signal quality for both was great (low -70’s to mid -80’s) and signal strength also improved from the low 20’s to the mid 50’s. We disabled WDS and the signal quality improved to low -80’s to mid -90’s.
This morning, we added a third client top the upgraded AP and suddenly all 3 900 Mhz. clients became very unstable. flapping up and down every few seconds. We have 6 more clients that need to be upgraded and added to this particular AP, and have 2 other AP on this tower with about 30 more clients on those (all of them are also 900 Mhz.) but can’t until we find out what’s causing this instability.

We tried everything we can thing of but so far, no matter what we try on the settings, nothing helps.

Any Ideas? has anyone else experienced this sort of problem?