Further update…
Tried reducing the cooking time to 18 minutes today and while it was significantly better, there were still more dud prints than I’d like.
It occurred to me that we used to print our mums 3 up on an A4 sheet and switched to printing on 98mm x 238mm sized sheets. We also switched from Epson Ecotanks to a Sawgrass SG500 a while back.
I did a test run of 48 mugs (3 oven loads) printed 3 up on an A4 sheet and printed on the Epson printer instead of the sawgrass. All 48 mugs came out of the oven perfect.
So, it seems the issue is either the sawgrass printer/ink OR the paper being too long.
Next test over the weekend will be to try longer sheets on the Epson printer and A4 sheets on the sg500.