Galaxy S10 Deep Sleep Bug is Related to VoIP.

Over on the XDA Developers forum, an issue has been raised about a bug in the proximity sensor. Some users have complained that after placing a voice-over-IP (VoIP) call, their Galaxy S10 handset fails to enter a deep sleep state.

It appears that it happens after using programs like Skype or WhatsApp to place a call. Since the Galaxy S10 fail to enter the deep sleep mode afterward, and drains the battery much faster than otherwise. The temporary solution is restarting the phone.

"I can confirm that... After finding why I have massive standby drain and blame few apps for that, now I know this is an issue with Voip calls. Reported trough Members app already," a user wrote.

Several others also had similar complaints. The one common thread of this failure is  tied to the Galaxy S10 powered by Samsung's own Exynos 9820 processor used in overseas versions of the Galaxy S10. Other models running on Qualcomm's Snapdragon 855 hardware appear to be unaffected.

Another thread on the same forum mentions that a solution from Samsung is on the way; 

"A friend of mine received a reply from Samsung telling that they have acknowledged the deep sleep issue, and it will be fixed in the next update (ASC1). So everyone please be patient, don't return your phone yet"