When you use Grand Totals to set the Allocation for Staff in a project, you observe unexpected behavior like some values getting wiped after being entered, some accepted but not assigning the expected values in all the periods, or some other symptoms.
Any supported Clarity release.
The project finish date may be higher than the maximum date in Clarity (around year 2079 or higher).
Check if any project/task/staff date (typically project Finish date) exceeds the maximum date in Clarity and modify those to stay within the supported date range.