tic tac toe

You missed some signals from your processes again:

Rst_n is missing from the FSM_Process (async resets must be in the sensitivity list)

C_pos is missing from COLUMN_process_comb.

You also have a problem with this last process - you are going to infer latches because you do not assign all nxt_st_C entries in EVERY branch. You cannot have a "null" in an combinatorial process either (because you wont be assigning the signals). I suggest making this a synchronous process, or putting default assignments at the top (and holding state is not a valid option, because that is what a latch is - you need to assign everything in EVERY branch to an explicit value).