Why WhatsApp spontaneously starts a backup in the middle of the day?

Question

It happens once in a while - I'm using WhatsApp (far from backup hours) and it just starts backing up and not letting me to use the app for several minutes.

The last backup was successful and finished hours before it happened, and after that backup popup message, it didn't backed up to Google Drive as usual - so only a local backup.

My guess was that it's kind of "flushing the buffer" to save the current state, maybe as a result of too much new data since the last backup.

Why and when does it happen?

Anything to do about it? (Except from killing the app)

Thanks!

EDIT: Added two more screenshots. It keeps happening and also with the Google Drive backup.

Device: LG G5, android 7.0, custom ROM, no root

— arieljannai | Sources

Answer

I finally think I found out.
It is connected to date/time as aBochur suggested, but it's not that I changed the date/time of my phone or moved between time zones.

My findings

I have LG G5 and it has a removable battery.

Whenever I takeout the battery and replace it with the second one, when the phone comes up it has an old date/time - can be hours or days before (not sure what's the rule here, maybe previous shutdown?). This, from some, reason triggers a backup on WhatsApp.

Times after startup:

After 2.5m the phone reception is back and fixes the date/time.

After 5m WhatsApp creates a local backup.

Sometimes, not figured out when yet, it also triggers the cloud backup. If it will - it will happen (~around) 30m after the local backup.
- I think it has to do with the time passed from the last cloud backup, but wasn't able to test it deeply yet.

So, the conclusion is there's nothing to do with it, this is how WhatsApp works and it's backup get triggered after it recognizes a date/time change.

This is the notification that sometimes WhatsApp shows, there's not a full correlation between this notification appearance and the backup trigger.

Your phone date is inaccurate! Adjust your clock and try again.

Note: I haven't tried anything, this message just appears on those occasions.

The answer will be updated if I'll be able to collect more information about this.

— arieljannai | Sources

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