Weird error on Sede Electrónica, says fields in red are missing but there aren’t any

Hey ,

I’m filling out the reimbursement application for medical expenses (paid for treatment abroad, now claiming it back from Spanish social security). On page 2 of the form I hit continue and get the usual “please fill in the fields marked in red” error, but there’s nothing empty on the screen, everything’s filled in.

Tried a different browser, cleared cookies, double checked the dates, re-selected the dropdowns… nothing works, same error keeps popping up. Has anyone run into this? Not sure if there’s some hidden field that usually causes this or if I just have to go in person or send it by post instead. Any help appreciated, been stuck on this for a while.
Thank you in advance!