Notification delays are usually either network induced or device issues.
If your internet doesn’t have a good solid Upstream connection, you will get delays sending notifications from the homebase to the AWS notification service that Eufy uses.
If your phone has battery or background data optimizations, this can cause up to hours of delay on notify. The phone won’t be listening all the time, so it will miss the notifications. This is the easiest to check. Look for Power Saving Exclusions and give the EufySecurity app an exclusion. This will prevent the phone from turning off the Eufy app to save battery.
Also, check that the Eufy app has background data turned On.
Note: These are the Android settings that effect notifications. I believe that iPhone also has some comparable settings, but since I haven’t had an iPhone for quite a while, I can’t help with those.