I have a Field Pack Checkbox, with just a single option, inside a Matrix field.
I just updated to Matrix 2.5.10, Fieldpack 2.1.1 (from the outdated version), and EE 2.7.2.
The value of the checkbox inside the matrix field will no longer save. If I check the single checkbox, submit the entry, and then go back to edit the same entry, the box is no longer checked.
I currently can't edit any old entries in this channel because the value of the checkbox will be lost when the entry is submitted.
Any Field Pack Checkbox not inside of a Matrix still works fine. I have tried re-installing Matrix and Field Pack.