Bigger poop and eating more hay is as a rule not a sign of ill health, certainly not stasis. With stasis, poop decrease in size and amount. Since it coincided with the vet visit, I’m thinking some kind of stress-response (albeit manifesting in a somewhat unusual way)?

Normally if a bun changes his eating habits and stops eating certain foods, you’d suspect a dental issue. But that’s generally seen together with reduced fecal output, because the bun eats less overall.

I’d wait and see. It’s not an emergency or anything seeing that his poop is actually bigger and you know he’s eating the hay.

Sometimes buns do things we can never understand. F ex my Bam drank from a water-bottle for three years, I could always hear him drink in the night. He had back-up water in a bowl. One day he decided he wasn’t going to drink from a bottle anymore. I still change the water and hang it up for him as a back-up, but he hasn’t touched the thing in more than 2 years.