my external ssd photos library won't open after High Sierra update

I have just bought a new MacBook Pro and use the SSD removed from my previous 2011 MacBook Air as an external drive. It is in an OWC enclosure. Before updating my new MacBook Pro with High Sierra, I was able to just double click the photos library in the old MacBook Air external ssd and it would open perfectly in Photos on the new MacBook Pro. Since the High Sierra update on my MacBook Pro the external ssd photos library will not open in Photos 3.0. There is a message popup that also says repairing library but it sits on 0%. The only thing that has changed with all this is the High Sierra update on the MacBook Pro. Questions: 1. Is this problem likely to do with the change to the APFS filing system not allowing photos 3 to read my external ssd library any more? 2. If I boot my macbook pro (with High Sierra) to the old MacBook Air ssd and do a high Sierra update on that external drive (so both drives are on the same OS), should I again be able to access that external photo library? Thanks!