Mostly it happened because using wrong chemical to clean the screen. NEVER USE MINERALS SPIRIT TO CLEAN THE INK ON THE SCREEN. AND NEVER LET THE RECLAIMER DRIED ON THE SCREEN. Both will lockup the emulsion on the screen and cannot be reclaimed.
Use proper time to burn your screen. Underexposed screen trend to be harder to reclaim. A tip is after you washout the screen, sit it under the sun and let it dry. The sun will "re-expose" the emulsion to make it fully exposure of the emulsion.