The bid-ask spread gives you uncertainty in your pd estimate, and I think you should then (in IFRS9 guidelines) add conservatism to compensate for that uncertainty? Is that so?
Also, I expect CDS to give a skewed view on pd, there is probably more demand than supply for cdss?
So either the mid, or if you're forced to include conservatism because of model risk then pick the side that gives the highest pd.
IFRS 9 requires that there should not be any conservatism built into the estimates. Mid point would be a better way. Typically, banks are modeling PD, LGD and EAD for both IFRS 9/CECL