Nick here from Shopify.
This does sound quite strange alright. Would you be able to try adding the apps via an Incognito tab and see if it works then? If it doesn't, my guess is it is a caching issue. Could you try clearing your browser cache and then double check if it's still happening? There is a great guide on how to clear cache here.
If none of the above work, not to worry, can you reply and let me know here and we can take a closer look into it and what might be happening.
All the best, Nick
If the private mode or incognito tab isn't working for you, I would recommend clear your browser cache and seeing if it works then. Could you try that and let me know please?
You can see how to clear your cache on a mac via the YouTube tutorial below and for all devices here.