flickering Bit

Dear All,

I put online the PLC with the PC to check step by step my program and I found that 3 exclusive BIT (coil) are flickering and not enable the contact; to be more clear the function part has to do 3 individual string check and this check is always enabled; I saw that the BIT status switch very fast between 0 and 1; the operands after (store, inverted contact, coil, reset) are ok.
I use this BIT only in this case; they are not called in other position...when coils are active it has to load a specific screen...I have set this function by Action menu...and It doesn't work!