No sound is playing.

The current settings are as follows:
Sounds play for the 1-minute-remaining mark,
but sounds do not play for the intervals between 60 minutes and 2 minutes remaining. 

"Alerts": {
"InGameWarningTimes": [
60,
30,
15,
10,
5,
3,
2,
1
],

Hey, that's fixed in the current version (5.1.0): the alert sound plays at every minute in InGameWarningTimes, not only in the last minute. Update and it's gone.

Since 4.0.0 the plugin needs the CrashExtensions DLL. The zip includes it, or drop in CrashExtInstaller.cs and run crashext.install. Your 3.9.3 config carries over, and the old one is saved as a .bak the first time it loads.