Custom ringtones stop playing after 3 seconds on iPhone 14 with iOS 18.1.1

iPhone 14, iOS 18.1.1

Calls from contacts with custom ringtones assigned to them only play the ringtone for about 3 seconds. The call is still actively incoming, and I can answer it, but there is no ringtone after the initial 3-5 seconds.

Factory ringtones and alerts/alarms work fine. Only the custom ringtones quit audibly playing a few seconds in. This has been going on for a couple months now, so during iOS 17, but continues now with iOS 18.

If I go to the settings and choose the custom ringtone, it plays fine, so the files are working.

I have checked the accessibility settings and they are set to automatic.

How do I fix this issue?

[Re-Titled by Moderator]