I use QField 1.9.6 on Android 10, QGIS 3.20 and QField Sync 3.4.4 on Ubuntu 20.04.
I have a fairly simple geopackage to edit with QField from QGIS. It is set as offline editing. Producing the package goes fine and there is no problem to edit it in QField.
I noticed that
data.gpkg-wal are present as soon as I open the .qgs project in QField and they do not disappear afterwards, unless you open another .qgis project in QField. Restarting the device as suggested does not wipe them. A finalizing edit button in QField to close every project would make sense.
But anyway the sync does not work, either with or without the presence of the
data.gpkg-wal files. If I open the
data.gpkg in QGIS, the changes are there, but the sync just fails. I did not change anything in the project in QGIS between the packaging for QField and the Sync.
I have exactly the same issue than QField QFieldSync issues and I tested the proposed solution, but it does not work for me.
The logs only show the following:
QFieldSync : Opened original project /mytreefolder/Qfield_whatever.qgz
Hard to say if this is supposed to be normal or not.