davem_or has given you the most probable reason.

I don't own one, but do own a number of modelling amps. Prima facie it appears that Fender have made their software clever recognise that amp model is unsupported, but not clever enough to present other than a generic dialogue to the user inferring that.

On that premise my advice would be to leave it alone until after you've researched everything you can about the issue including emailing Fender product support, checked the Fender forums (?) for a FAQ, and spoken to other LT25 owners, or risk bricking it if you somehow manage to force it to download new firmware it shouldn't which will really cause you a headache.

Until you can, it's working, leave it alone. GL with your quest.