If any of those are android users, it may be down to the non-android standards friendly battery optimisation the manufacturer ship their devices with (e.g. Samsung, Huawei, OnePlus, Xiamoi, etc.)
I've had more issues with missing notifications on my OnePlus than I ever had on my Pixel (I have list of reasons why I'll never buy Google hardware again, mostly coming down to their support). Most issues get fixed by me persuading OnePlus to stop applying their secret sauce to power control