Macro assigned to buttons get removed automatically on reopening Excel file

 Please refer this link wherein the same issue has been discussed: 

Link (copy/paste in browser)
https://techcommunity.microsoft.com/t5/excel/copied-a-macro-enabled-workbook-into-onedrive-now-macros-cannot/m-p/3277944

Notes
From the aforesaid, we understand that you may have to add the ONLINE ONE-DRIVE location to "Trusted locations".

Steps

1. Start Excel. 
2. File >> Options >> Trust Center >> Trust Center Settings >> Trusted Locations >> Add new location >> "Add the ONE-DRIVE folder"
3. Also, check the option "Allow Trusted locations on my network (not recommended)" as suggested in the aforesaid link.