Alcatel devices are notorious for their aggressive battery "optimization" so we have to exempt Manage SPIN from this aggressive battery optimization. Unfortunately, there is no documented method to exempt the Boomerang Accessibility Permission so that it "sticks" and does not get "optimized" (shut down in the name of saving battery power.)
NOTE: This issue affects ALL Apps that use the Accessibility Permission so it is not just about Boomerang.
Check out https://dontkillmyapp.com/ which has extensive documentation.
Contact Alcatel Support and/or the vendor that you purchased the Alcatel device and see if they can help. Tip: When contacting them, state that ANY App that uses the Accessibility Permission is losing the permission - this way, they can't simply state that it is the "other" App issue. You can even mention App Lock which has 100M downloads.
If you have a solution:
Post it in the comments and help others! It would sure be appreciated by other Alcatel users.