I just opened a pro project that was created pre 2.5 upgrade. I can see my data as expected.
When I try to re add that table to that project or any other made after the upgrade we get an error.
FAQ: What characters should not be used in ArcGIS for field names and table names?
After looking into it, I believe that the error is because pro is adding quotes to field names. Only on the layers that have a _ before hand. This did not happen in a pre Pro 2.5 project and does not happen in desktop products. I downgraded to 2.4 and the table added without the quotes.
We do not have access to the database and cannot change the field names.
Any suggestions on a work around?
What is the source of the table and how are you connecting to it?
A table from a SQL server.
And maybe it is the new normal...
although the applicable software list is ancient
Software: ArcGIS-ArcEditor 9.3.1, 9.3, 9.2, 9.1, 9.0, 10 ArcGIS-ArcInfo 9.3.1, 9.3, 9.2, 9.1, 10 ArcGIS-ArcView 9.3.1, 9.3, 9.2, 9.1, 9.0, 10
From your link
Do not start field or table names with an underscore or a number.
I am not sure why it was created that way but I cannot change the field names on the database at this point.
There is a new sql odbc driver that took care of excel and sql problems for me once I installed it:
I installed the new driver and it did not work.
Unfortunately we are not running SQLite.
I'm not using sql lite either.
Just because it worked in previous versions, doesn't mean its supported. Try running Validating table and field names in Python—ArcPy Get Started | Documentation
Also see
FAQ: What characters should not be used in ArcGIS for field names and table names?
Fundamentals of adding and deleting fields—Help | Documentation
Naming Stuff In ArcGIS - USGS OEI/Enterprise GIS - myUSGS Confluence
When I try to create an attribute in 2.5 starting with "_toast", not only does it create "_toast", "f_toast" gets created as well, which is odd. Perhaps this is one of the several new bugs that were introduced with 2.5.
I recommend opening a case with tech support. I think you're out of luck on the quotes thing, but I'm curious as to their response both on existing fields created pre-2.5 that start with "_", as well as what's going on when you create a field in 2.5 starting with "_" and why a second one gets created with "f_".
And...when you initially submit your case, please include EXACT steps to reproduce