Google Pixel and Pixel XL owners are being plagued by a mysterious data backup issue. Many are having trouble uploading certain items — including text messages, call history, and apps — to Google’s servers, but the company promises it is investigating the issue.

Despite having Google backup enabled, some Pixel users have found that certain data cannot be saved. Some items read “Waiting for backup,” and there appears to be no way to fix the syncing issue. Users have tried disabling and re-enabling backup, restarting their device, and even powering it up in Safe Mode — but nothing fixes the problem.

Some owners report that they’ve been experiencing this issue ever since the Pixel series made its debut last October, so it’s not a recent problem.

“I recently wiped my device and lost all of my call history because it wasn’t backin [sic] up,” writes one user on the Pixel User Community forum. “Like most people, I assumed it was backing up like everything else. SMS and device settings restored without a problem. Call history was apparently waiting to backup since I turned on my Pixel in November.”

Google says it is now “actively working on this issue,” and community managers are now reaching out to some privately in an effort to obtain bug reports that might identify the root cause of the problem. Hopefully the company will have a fix ready soon.