[jp.naver.line.android] LINE does not receive push notifications

Affected app
Name: LINE
Package id: jp.naver.line.android

Describe the bug
Push notifications are not received.
App appears to be registered in MicroG control panel, but never receives messages.
LINE reminds user about turning off battery optimizations, but it does not actually run in the background. This is not observed when using a system with Gapps.

To Reproduce
Steps to reproduce the behavior:

1. Set up MicroG as usual, with registration and cloud messaging
2. Install Line and log in.
3. Have someone send a message.

Expected behavior
It should receive push notifications

System
Android Version: 12
Custom ROM: Unofficial Lineage OS 19

microG
microG Core version: 0.2.27.223616
microG Self-Check results: All ticked

Additional context
All other apps using push notifications work as expected. This appears to be a known issue, as I've seen a few threads in Chinese language forums reporting the same. LINE is widely used in several East Asian countries, such as Japan, Taiwan, and Indonesia. Not having push notifications severely hinders the usability of MicroG based systems for users who are expected to respond to messages promptly in these countries.

The report names no source file, test, or entry point. Start by reproducing the issue with LINE on Android 12 and unofficial LineageOS 19 using microG Core 0.2.27.223616, then trace the cloud-messaging and background-execution path; done means LINE receives push notifications under the reported setup.