It is much deeper than tactics.
He refuses to put in long yards in practice.
He is also dead set against practicing his return of serve.
He really can't break a decent player.
Even Fognini would have beaten him again today.
He is losing for only one reason now: he doesn't care to put in the required 7-8 hours on the practice courts to bring his game back.
Should a 9 times RG winner with 46 clay titles be struggling against anybody on clay, let alone wawrinka?