VSTO Add-In: OleObject of type Forms.Label.1 is not accessible in Excel build Microsoft 365 MSO (Version 2402 Build 16.0.17328.20124)

Question

Hi,

We have a VSTO add-in (almost 10 years old) which stores some metadata in an OleObject of type Forms.Label.1 in an excel workbook.

Recently we came across a user who has the following issue (user has recently updated excel to Microsoft 365 MSO (Version 2402 Build 16.0.17328.20124) 32 bit):

1. When the user A tries to open a workbook whoes author is a different user B, the add-in installed in user A's excel is unable to read the data from OleObject of type Forms.Label.1 and an exception "(0x800A03EC): Unable to get the Object property of the OLEObject class" is raised.
2. The same workbook (created by user B) open perfectly and the add-in is able to read the data from OleObject of type Forms.Label.1 without any issue in another user's machine who has Microsoft 365 MSO (version 2401 Build 16.0.17231.20290) 32-bit. We also tried it on different builds like Microsoft 365 MSO (version 2308 Build 16.0.16731.20542) 64 bit and it works fine (it has been so for last 10 years :)).
3. When the user A creates the workbook themselves i.e they are the author of the workbook, and they create the OleObject of type Forms.Label.1 using the add-in, then they can read the metadata from the OleObject without any issue whenever userA reopens the workbook.

Things were working correctly prior to the upgrade.

So somehow the issue seems to be related to accessibility of OleObjects if the author of the workbook is different.

Thanks in advance,

Abhijit.