Steps to reproduce:

1. Switch between two synthesizers several times and wait a bit. I was able to reproduce this reliably using ESpeak and Vocalizer, but it may happen for other synths as well.

Actual behavior:

A traceback is displayed. The following log fragment demonstrates me switching from ESpeak to Vocalizer and then getting the traceback.
INFO - synthDriverHandler.setSynth (09:26:49.664) - MainThread (2068):
Loaded synthDriver espeak
DEBUGWARNING - synthDriverHandler.getSynthList (09:26:52.441) - MainThread (2068):
Synthesizer 'mssp' doesn't pass the check, excluding from list
DEBUGWARNING - external:synthDrivers.vocalizer_expressive._voiceManager.VoiceManager.setDefaultVoice (09:26:54.850) - MainThread (2068):
Voice not available, using default voice.
DEBUGWARNING - external:synthDrivers.vocalizer_expressive.SynthDriver._set_variant (09:26:54.855) - MainThread (2068):
Model not available: full_155mrf22
INFO - synthDriverHandler.setSynth (09:26:54.856) - MainThread (2068):
Loaded synthDriver vocalizer_expressive
ERROR - unhandled exception (09:26:59.835) - MainThread (2068):
Traceback (most recent call last):
File "wx\core.pyc", line 2196, in Notify
File "nvwave.pyc", line 349, in _close
File "nvwave.pyc", line 90, in _winmm_errcheck
OSError: [Errno 5] The specified device handle is invalid.

Expected behavior:

No error.

System configuration

NVDA installed/portable/running from source:

Installed.

NVDA version:

alpha-20718,633435db.

Windows version:

Windows 10, version 10.0.20185 Build 20185.

Name and version of other software in use when reproducing the issue:

N/a

Other information about your system:

N/a

Other questions

Does the issue still occur after restarting your computer?

Yes.

Have you tried any other versions of NVDA? If so, please report their behaviors.

Yes, this seems to have started when #11024 was merged.

If addons are disabled, is your problem still occuring?

Yes.

Did you try to run the COM registry fixing tool in NVDA menu / tools?

N/a.