iphone iPhone 6 with iOS 10.3.3 storage keep filling up, despite no activity

[deck]

I've taken to Google to find an answer but have yet to find one that either applies to me or makes sense:

 

My iPhone 6 storage keeps filling up on its own.  Even if I don't touch the phone for a day, the available storage decreases.  This came to a head last week when I ran out of space on the phone; I hadn't installed anything in weeks, had only a few pictures, no videos, no voicemails, etc.  I use primarily WhatsApp, Facebook, Reddit, Gmail, Chrome, and Music.

 

This is the third time this has happened since I got the iPhone.

 

So I reset the phone and restored from iCloud on Monday.

The restore worked and the phone is now identical to how it was prior, except instead of having no free space it now had 6.4gb free.  

Later on Monday, the space was down to 6.3gb.  

Even later it was down 6.1gb.

On Tuesday it was at 5.94gb, then 5.9gb.

Today started at 5.89 and now it's at 5.83. 

I guarantee that when I check again later today and tomorrow it will have decreased again.

This is the same thing that happened last time;  every day I would lose between 50 and 100Mb of space.  After a few months, I will again be down to around a gig free, and it will keep falling.

 

No photos are syncing.  I don't use iCloud to backup pictures and video, those go to OneDrive.

I haven't taken any new photos or videos since the restore.

I haven't downloaded any additional apps since the restore and I even deleted an app after the restore.

Music is not set to sync and there is no music from iTunes, Music, or anything else.  I don't have any other Musics apps.

YouTube hasn't been used since the restore.

Chrome has seen minimal use.

Multiple apps are set to not use background refresh.

 

Can anyone shed some light on this?  It's odd.  It's been reported and discussed on various sites but no one can agree on the issue and Apple will not acknowledge if there is one.

 

Thanks!

[JustGeorge]

Since 10.3.3, I've been having a lot of problems with texts failing to send or the recipient not getting them for hours after being sent.

[deck]

 

Today it's down to 5.74; the only activity since this post was on WhatsApp, FB and Reddit. Somehow that's good for 100MB of leakage.