You said it hasn't cut through all the way, is that the whole piece or has it cut through in some parts but not others? When was the last time you checked your spoilboard, your machine spindle was trammed & the calibration of the machine?
If they are all good then the only other things I can think of to to check are your z zeroing & your collets, have you checked the machine is zeroing to exactly the same spot after the cut? If not then the bit could be slipping in the collet.
I like straight flute bits for plywood, they seem to give me a better edge finish than spirals but I am not an expert, I don't use commpression bits because of the cost, the amount of work I would use them for just doesn't justify the expence but if I were doing more work where they would be of benefit then I would certainly look at buying them