Strange aversion to the back garden?

[NavigatingAdulthood]

I just wanted to know if anyone has any ideas, suggestions or advice for how to deal with the following problem

I have a 2 year old Chow Chow. He has a history of gastrointestinal problems and has recently been on antibiotics after an awful flare up. Otherwise, no problems! Over the last couple of days, he's been refusing to go on the grass in our garden. I can lure him enough with treats to wee but nothing else. He whines to go outside but then won't leave the patio. However, when my partner takes him on a walk; he has an absolute blast and goes to the toilet - on public grass.

He's playful, eating well, still himself and we have no other concerns apart from this sudden strange behaviour.

Any ideas?

Has he had a painful poo in the garden and now associates it with pain?

A lot of times it can be noise related-my dog always wants to cross the road because there is a house that has a very high pitched cat deterrent I can't hear it but my young eared children can

Maybe a new alarm or something scared him and he now wants to avoid? He hasn't been stung/hurt himself somehow?

Has he gotten a fright from fireworks? (probably not if it has been over the past few days)

I'd give it some time and hopefully he will come round. My Ddog stopped wanting to walk through the town centre when she was spooked by a noise but eventually overcame it.

His last Gastro flareup was quite severe, probably the most severe that he's had which results in painful defecating/straining and rectal bleeding however when he has had these flareup before he has never followed it up with this behaviour.

My partner and I did assume that he was scared to go to the toilet in the garden as he's associating it with his last flareup but just thought it was strange as a few days ago he was able to go in the garden and go to the toilet and he didn't have a flareup then