I experienced the same on OSL-LHR-HND last week, where the boarding pass for LHR-HND disappeared once the flight from OSL departed. Luckily I had a screenshot saved, and also got a paper boarding pass printed while in transit.
I've later found that the SAS app (both old and new) shows the same barcode for all flights, similar to the paper version, so I could likely have used the one for OSL-LHR for the entire journey.
Last edited: 10. des 2022