Hi @nepos
Same happens to me this week with one of the 3 journals I still need to move to OJS 3.
I didn’t dig much into this, but you have to keep in mind that ojs 2.4 is really old so it’s normal things top working from one day to the next.
My workaround with this is downloading the xml and upload manually with the crossRef upgrade form.
But as said, please take in consideration that OJS 2.x is not supported any more by PKP so my recommendation is upgrade to OJS 3 as soon as possible.
Cheers,
m.