APFS Container Resize error code is 49187

Sorry, but there is no error code list for APFS from Apple. APFS is too new. Highly unlikely anyone here knows what that means beyond the obvious - container resizing. I would assume there is a problem that you can try to fix using Disk Utility if you haven't already tried. Try performing First Aid on the volume.

Repair the Drive for El Capitan or Later

1. Restart the computer and after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and press the Continue button.
3. Then select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid tab in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
5. Select Restart from the Apple menu.

If the above doesn't help then you need to reformat the volume.

See these articles File system formats available in Disk Utility - Apple Support

Partition a physical disk using Disk Utility - Apple Support

By chance do you have a Boot Camp partition on your drive? See Can APFS be used with Time Machine, Boot Camp, and File Vault?. Or it could be caused by Time Machine's snapshots.