I noticed this on my end as well.
Android 10, essential phone 1, last phone update was 1/2020 so a major phone update didn't change behavior on my end.
basically instant notifications on 2.2.3
Noticed delayed notifications (5-15 minutes) after upgrading to 2.2.4 which got slightly better after the 2.2.5 update. Still can be anywhere from 1-10 minutes delayed. If multiple notifications gets sent around the same time sometimes 1 gets lost/never delivered to the phone.
Was perfect on 2.2.3. Have rebooted my phone and cleared data/cache from he app several times. Fully rebooted he hub several times. Performance of hub otherwise seems normal.
All sleep/data/battery saver options have been disabled on the phone.
Only have 1 phone connected to hubitat currently, so cant compare performance on different makes/user accounts.