I have WhatsApp installed and signed in on both my phone (A35) and watch (FE), but notifications for it don't show on the watch. I have notifications for WhatsApp enabled, and show alerts even when phone in use enabled. It always used to work but hasn't recently. Also, I sometimes get random notifications on the watch for messages I got days ago. For example, a message from my friend sent on Wednesday showed on Saturday, for some reason.