Alright, I’ve been testing this as well, as I had inconsistent issues - I’ll just ping the last PD employee that really took a look at this issue and reported on it: @SarahChandler
Phone: Samsung Galaxy S20 5G
One UI: 3.1
Android: 11
PD app version: 6.53.1 (12039)
For all tests, I have PD set up on my work profile. However, I also have it downloaded on my personal profile, but it’s not set up in any way.
The PD contact is also favourited/starred on the work profile, and “Automatic Contact Card Management” is enabled.
Additionally, the PD app “HU Override System Volume” & “HU override Do Not Disturb” settings are both enabled.
For each test, I’m manually creating a new high urgency incident, and leaving the phone untouched until the first phone call should be made.
Baseline - Sound at lowest volume & DND off
This is the base use-case where sound should always work, given the phone has sound enabled.
- System volume on sound & vibrate;
- Volume at lowest non-zero value;
- Do Not Disturb mode disabled;
- Notify app immediately;
- First call to personal & work phone after 1 minute.
As expected, PD & calls worked fine this way.
This of course makes sense, since sounds are on globally for the whole phone. If PD didn’t work in this situation, I’d be very concerned.
Still, it is important to set a baseline, and confirm it indeed works as we expect it to. 
#1 - Desired use-case: Vibrate & scheduled DND turned off during most hours
This is how I want PD to work on my phone, and these parameters will be the base of the rest of my tests.
- System volume on vibrate only;
- Volume at 0;
- Do Not Disturb mode disabled (scheduled to turn on at night, however);
- Notify app immediately;
- First call to personal & work phone after 1 minute.
This did not work as expected.
The PD App notification correctly caused the phone to vibrate + make a sound.
However, the phone call only caused the phone to vibrate.
#2 - Vibrate & Do Not Disturb enabled
- System volume on vibrate only;
- Volume at 0;
- Do Not Disturb mode enabled;
- Notify app immediately;
- First call to personal & work phone after 1 minute.
This worked as expected.
The PD App notification triggered both vibration and a sound.
The phone call also caused the phone to vibrate, and the ringtone to be played.
#3 - @max.2 's solution, with a phone call immediately being made, Vibrate & DND off
- System volume on vibrate only;
- Volume at 0;
- Do Not Disturb mode disabled;
- Notify app immediately;
- First call to personal & work phone *immediately.
This did not work for me, unlike what @max.2 reported.
Notification did vibrate + make sound.
Call only vibrated, just like before.
#4 - @max.2 's solution, with a phone call immediately being made, Vibrate & DND on
- System volume on vibrate only;
- Volume at 0;
- Do Not Disturb mode enabled;
- Notify app immediately;
- First call to personal & work phone *immediately.
Test successful, just like #2.
PD App notification vibrated + made a sound.
PD phone call vibrated + made a sound too.
So once again, DND seems to have to be on, and the time when the call is made does not matter.
Conclusion
It seems that DND mode is the key to the issue here. With this (limited) testing it is clear that the “HU System Volume Override” setting only works if the phone is also in DND mode.
Oddly enough, PD App notifications always make sounds just fine, regardless of if DND is on or not. Thus it seems this is an issue moreso related to starred contacts/phone call ringtones in general, rather than notifications overall.
The fix proposed by @max.2 did not work for me, and without DND enabled, this “immediate-call” approach still did not work for me to create sound. So once again, DND mode having to be enabled for system volume override to work seems to be the problem at hand.
Retrospect
As stated in the desired use-case, I now run my phone on a schedule, to turn DND mode on during the night, because of this exact problem with PD. However, eventually, I just want DND mode turned off fully again. It’s simply a compromise I’m willing to live with for now, so I at least get woken up at night if a HU alert comes in.
DND seems to have to be enabled in order for PD’s calls to make a sound if the phone is in silent or vibrate-only mode.
However, during the day, I don’t want DND mode turned on, so this still results in calls only vibrating during the day (as I do want my phone to run in vibrate-only). Of course, I’m more likely to notice the vibration during the day, when I’m awake, but this is still very problematic.
I don’t want to be required to run my phone with DND turned on or with the volume turned on during the day, to fix thus.
I simply want my phone on vibrate-only during the day, and only have PD’s app & calls to override the volume and make a sound, so that all other notifications (e.g. chat messengers) & calls on my phone stay silent and just vibrate.
I hope my tests and reporting can help the PD team to pinpoint the problem and resolve it. This issue has been running for much over a year now, and although I understand this probably has to do with a lot of possible brand + android version combinations, I do see this as a very urgent thing to fix.