Cannot resolve the collation conflict between "SQL_Latin1_General_CP1_CI_AS" and "Latin1_General_CI_AI"
Let's see about the possibilities. The first one is that server's collation has changed. This is very unlikely, as it requires rebuilding system databases. Unless you have extremely dynamic environment with multiple admins doing stuff in chaotic manner, I wouldn't consider this further.

First and one half: is it possible that the database has been moved to another instance? If you are using client-side aliases, the change can be transparent.

The second one is that database's collation has changed. This is quite straight-forward, all one needs is an alter database command. So, check the database's current collation and expected collation. Do they match?

The third one is that the stored procedure itself has been modified or renamed. Maybe there used to be explicit collation specification, but that was dropped. Do you have sprocs in version control?

To see the last modify dates for stored procedures, query sys.procedures

SELECT create_date, modify_date, name
FROM sys.procedures;


As far as I know, without auditing it's hard to catch database changes after the fact. If you are using some kind of CI system, double-check if the database - or sprocs - were re-deployed recently. 

It would be worth a shot to chat with other server admins and developers too.