Please send me in the correct direction.

A few problems here.

First of all, the case statement in the process is not inside the clocked part of the process. This is bad practice, as if you really meant it to be asynchronous logic, it should be in it's own separate process. The fallout is you have many signals missing from the process sensitivity list.

The way the code is, you are creating many latches - for data_out_a/b/c/d and the signals a b c d. I highly suggest you separate these processes first or put this code inside the clocked part of the process.