Re 1 - are you perhaps using a custom sound and have not given Glimpse the permission to access files on your phone?
Re 2 - You probably have checked to obey system DnD in Quiet Times.
Thanks for your reply!
1. I hadn't realised I had to manually set that in Settings>App permissions>Storage. Thanks.
2. Obey DnD is ticked, as was "Enable quiet times" in Glimpse. I now understand that it was the latter that was preventing visual notifications during DnD. However, with only DnD enabled, Glimpse shows visual notifications, as I desire, but also vibrates the phone during DnD. Shouldn't vibration be muted along with sound?