Amount is Reset to Zero When Updating

1) Appears to be a conflict with ThemeFusion Core Plugin for ThemeFusion Themes.
When it’s activated, this problem occurs:
I put in a line item with quantity and rate and the amount is calculated correctly. THe invoice totals are updated correctly. However, when I click UPDATE, then the line item amount is set to zero along with invoice totals. When I look at the list of all of the invoices, the Total is correct.

2) When I click Add Another Item, nothing happens.
This was happening prior to updating to 3.8.12.
WordPress version is 5.5.
This occurs even when all plugins are deactivated.