Thanks @fxholl, I was now able to see the problem!
I’ll play around with this some more to try and understand when exactly this occurs (I suspect it might be similar or even related to this issue).
In the meantime, seeing this appears to affect just the preview but not the actual execution, perhaps you simply want to add a Set node in front of the If node in question reading this value for you? Like so:
The preview on the Set node will still fail, but it’ll return the correct value:
You can then use this new field inside your IF node for building your expression with a working preview:
