(Not answered)
Giant TCR Advanced
"The wheels . . . are set up tubeless though – Giant supplies ready-to-go tubeless so that all you need to do yourself is to add the sealant, since that of course has a shelf life."
What's the betting that there's never been any sealant in either tyre?
On the plus side that'd mean that taking a quarter of rim off would be easy enough and pour some sealant in. And of course the rear tyre may not have any sealant in either - so do that one too.
What drop in pressure do you get over a few days in the front tyre?