Just letting users know I have reported the following bug on the Bug Report Form in case you are experiencing the same issue:
Cannot login to the Bubble Account iOS App using iPhone 5S OS 10.3.1. Update: Affects any iOS device using 10.3 if you are using login components in your app.
I am not sure, but does this also affect devices older than 5S. I heard that Apple are forcing 64bit architecture, and are no longer support updates to 32bit devices.
@emmanuel here is a suggestion for fixing this issue (It`s a major issue due to the widespread of iOS 10.3.
The trick would be to use the following plugin to set the cookievalue and fetch/use it for all subsequent calls. Possible one might need to intercept ajax calls using a replacement function for the original ajax calls the inserts the value on each new request.