After trying every option I finally gave up and decided to go back to my iPhone X. The Galaxy S10 now lies in a drawer waiting to see if some day this will be fixed (probably not).
Not so sure Samsung deserves the bashing here as it's more of an Android issue(Oreo & Pie). I recently purchased an S9 and yes it has the delayed notifications like my S7 & Chuwi Android tablet. My Ipad does not have the issue. I work around it by disabling idle/deep sleep mode using the ADB method. Still not as responsive as the Ipad but tolerable. Maybe some opinions from LG, Huawei, Oneplus owners need to be checked out. Mine started with the Oreo update last summer on my S7.
Same, s9 for a yeas, s10 plus is doing it even more frequently. I have done literally everything mentioned in this thread.
One thing that does work is being constantly on VPN
My wife has Galaxy A8, and she doesn't get notifications at all, WhatsApp messages are constantly delayed as are viber and messenger messages. I don't know if Huawei has the same problem but I'm planning to switch.
I have had this problem for over 2 months now and it's not getting any better I have tried a few fixes but none have worked.Cant believe Samsung is ignoring the problem especially with the price of these phones.