launch template suddenly stopped working

Hi, I have a simple launch template that fires up an instance based on an AMI built through Image Builder, which also distributes the ami to the template as a new version. All was working fine until yesterday when a colleague tried to launch an instance and it wouldn't proceed unless I put a value in for IOPS on the gp3 root volume. This is new. Previously it just went with a default for gp3 (3000) - now it has to be specified. I checked previous known good versions of the template, and they also displayed this change in behaviour - this rules out a change on my side. I also checked cIoudtrail to see if anyone else had changed anything - they hadn't. I have got my stuff working again, by removing 'gp3' as a volume type, but this seems to be an undocumented breaking change that I only picked up due a bit of ClickOps. What gives?