The 'FieldValueError' is seen only in the Android app in certain circumstances when a video or audio is present. Our team are aware of this and preparing a fix.
In the meantime a workaround to save the glog can be successfully performed by taking the following steps:
In glog edit mode:
1. Double tap on any audio or video present on the glog.
2. Select the sound option and change the volume to any value less than 100.
Now exit and save the glog. The glog will now sync successfully.