Pruning iOS “System Data”

I've had System Data balloon to over 30G+ over the course of a month (iPhone XR, current iOS).
It got rapidly worse after buying an Apple Watch and turning on sleep tracking, to the tune of System Data expanding by about ~1G PER DAY.

It's got to be something other than text logs, because they should compress well and not grow that fast.

And there are really two bugs here:
1. too much accumulation of something
2. that something NOT getting purged when the device is full. My it maxes out my storage I cannot open Mail or the camera.

It's enraging to have to do this unpair/backup/erase/restore/re-pair dance every few weeks.

iPhone SE 1st gen, 128Gb, do not sync anything to iCloud ever. 63Gb of System Data. PC backup is ~25Gb.

Probably erase&restore backup from PC will resolve the problem (contrary to suggested solution on Reddit), but I do not want to lose Signal app history.

@stranger, I had a similar problem.

TL;DR: It was a spurious 8GB folder of thumbnails that Photos left around and couldn’t delete. I deleted it manually with a utility app and it’s been good since then.

My iPhone SE 1st Gen also kept running out of space.

Photos was the largest user of space and even after disconnecting my photo library from the cloud and deleting all photos, Photos was still using over 8+ GBs of space.

After a backup and restore, the same problem persisted.

Since Photos should have been empty at this point, I went in with iMazing (other utility apps work too, apparently) and found a spurious ~8GB folder of thumbnails in Photos. It must have somehow escaped the internal cleanup procedures and I think the file modification dates were months old. I think the folder was next to the Photos database files.

After deleting that spurious folder, I re-enabled the iCloud Photo Library sync and since then Photos has been working fine and no more ‘out of storage’-type errors since then.

I probably could have blitzed the entire Documents folder in Photos and presumably Photos would have rebuilt it, but I was cautious.

Might be worth seeing if there are duplicate thumbnails folders in your Photos library. I think iMazing might be free for that function. I read iExplorer might also do the job.

Has anyone (Oakley?) dug into this? Is there a list of paths included in "System Data"? Can some of those be seen by a third-party utility? Does sysdiagnose give any insight?

I have this same issue. I got my kids iPhone SEs with just 16GB of storage to use for basic purposes. Mostly they can't even upgrade because have the storage is "System Data" that can't be purged. When I manage to upgrade them, the usage goes down for a while but then creeps back up.

Usually it'll say things like Photos is using a lot of space, even though Photos has no photos in it. Or Messages will be taking a lot of space, but there is no way to find what in Messages is the issue, and no way to delete all the non-text.

Absolutely infuriating.

I have 10 Gb of music data even with zero songs, there is no way of getting rid of it, even deleting the music app, does anyone knows how free the space?

That reminds me of a related issue about 1-2 years ago when Photos sync kept transmitting the same image or video again and again, failing at it, and racking up my mobile data volume over 1GB per day, as soon as I left my home - and there was no way to tell iOS not to sync these items during a mobile (non-WiFi) connection. I only could disable Photos sync entirely.
Had to erase and re-sync the entire photos lib. At least that was an option :) This System Data issue seems even worse, and more widespread.
Though, my issue was costly due to me exceeding my data volume, and Apple's support refused liability - I mean has anyone ever gotten gifts of goodwill (such as a free month of Apple Arcade or something) for the hassles Apple's "small" mistakes make us go trough? Never heard of it.