SQL Server : weird Invalid object name - sql

Question

I am trying to create a stored procedure and I get this error:
Msg 208, Level 16, State 6, Procedure SP_MergeStagedPoliticalPartyAgents, Line 1 [Batch Start Line 0]
Invalid object name 'SP_MergeStagedPoliticalPartyAgents'.
SQL is as follows, minus the content
CREATE OR ALTER PROCEDURE SP_MergeStagedPoliticalPartyAgents
AS
BEGIN
-- Content removed for brevity
END
If I alter the name in anyway, i.e. adding an extra s, or removing the s at the end. It works 100% fine, so my question is what is it with this particular name that I am using that is causing it to fail?
Does SQL Server have a name validation regex that this name is violating? Is it a reserved name?
Weirder addition IMO: for the sake of testing if I go:
CREATE PROCEDURE SP_MergeStagedPoliticalPartyAgents
AS
BEGIN
-- Content removed for brevity
END
It runs fine and creates the stored procedure on top of that from then onwards the CREATE OR ALTER PROCEDURE SP_MergeStagedPoliticalPartyAgents statement works fine.
It seems as if a stored procedure with this name doesn't exist it will fail on the CREATE OR ALTER PROCEDURE SP_MergeStagedPoliticalPartyAgents but pass on the CREATE SP_MergeStagedPoliticalPartyAgents if it is being initialized for the first time.
Note:
I already have other stored procedures created in the same mannerism that are fine
It is not a permissions issue as I am able to create stored procedures fine.
Running the script via VS causes the same issue so it is not related to SMSS
It also isn't the content. If I replace the content with a basic select * from table it still has the issue.

Answer 1

Just after I posted the issue, I found the solution.
https://bornsql.ca/blog/remember-this-if-you-want-to-use-sp_/
Create or alter
You can quite easily create a stored procedure with the prefix, both in the master database and any user databases you have, using CREATE PROCEDURE. However what Erik shows is that if you already have a stored procedure with a name that has the sp_ prefix in the master database, and then use CREATE OR ALTER syntax to create a stored procedure in a user database with the same name, you’ll get an “Invalid object name” error in the user database:*
I found that someone had created these stored procedures in the master database also.

Answer 2

I've got the exact same issue. SQL 2019 (15.0.4053.23)
I have run the exact same stored procedure on another database with no issues, yet on this particular database it errors. Changing the name works, removing the ALTER and only using CREATE works. if I CREATE the procedure and then use CREATE OR ALTER, it works.
CREATE OR ALTER PROCEDURE dbo.sp_bt_annl_stmt_members_select
AS
SELECT * FROM sysusers
Msg 208, Level 16, State 6, Procedure sp_bt_annl_stmt_members_select,
Line 1 [Batch Start Line 0] Invalid object name
'dbo.sp_bt_annl_stmt_members_select'.
CREATE PROCEDURE dbo.sp_bt_annl_stmt_members_select
AS
SELECT * FROM sysusers
Commands completed successfully.
Running the CREATE OR ALTER again works
CREATE OR ALTER PROCEDURE dbo.sp_bt_annl_stmt_members_select
AS
SELECT * FROM sysusers
Commands completed successfully.