Welcome to YT! I have heard this before, potty training mishaps after neuter/spay. Perhaps surgery temporarily affects their ability to feel and control their bladder muscles.
Supervise your boy as closely as possible. When he potties on the pad, praise him profusely and maybe give a small treat. Never stop giving praise.
Clean the accident spots with an enzyme cleaner to get rid of the scent so that he won't be tempted to return to the spot.
Hopefully Taco will be back to his good potty ways soon.
