Yes I know it works on android 6. Problem is with android 5. Sorry for this read-only manifest. It remained after AndroidManifest.xml modification tests.
I have tested app in the way you do - with #StartAtBoot: true in service and read-only prosperity switched off - so B4A can use it's own AndroidManifest.xml.
Of course everything seems ok inside (permission, service ,receiver) but unfortunately in not start after reboot. Several other apps /e.g.. PixelPhonePro/ starts flawlessly and their processes appear as working after phone restart.