Thanks Jeff,
I’ll submit a bug report.
What has worked is enabling IsUsingAudioMixer = 1 in the console. By default, this must be off.
Reverb is now working, only when sounds have an applied attenuation.
I’m not sure if this is intentional and has something to do with the transition to the new audio engine but it seems to have fixed my issue.
Enabling this is causing a few crashes here and there, but at least the reverb is working again.
Dave.