Hello @Matt Clarke and welcome to Microsoft Q&A.
Could you please tell me which region the Integration Runtime is in, and which region the Data Factory is in? Not all regions are supported in this.
Also, I had a Factory in West US, where the Integration Runtimes in Managed Virtual Network were in reporting the same message as yours. They had been sitting stale for a month. Just now I refreshed them by clicking the repair button. After a while they went green. Whatever caused them to fail long ago must have been fixed and they just needed a restart. This probably isn't the same as you case, as mine were stale.