Unable To Open The Search Page

This is a summary of the situation:

Topic	Comment
Issue	Not being able to access `/dev` of a project. Browser console shows 404 Not Found
Worked before?	Worked for months
Caused by a user-initiated change?	To my knowledge, there was no change to the code nor settings of the project. There is no other accessing the code of the project. Not sure if some change happened to the spreadsheet
Project location	The project's container is a spreadsheet
Project type	GCP default
Deployed	Execute as me + Who has access anyone
Permission	I am not the owner of the spreadsheet. I am able to edit and share the spreadsheet. The owner holds @gmail.com type of account. The owner is not able to access `/dev` either
Script role	My role in the script setting is an editor
New deployments	I am able to create new deployments. New and existing deployments can be access by their URLs. But `/dev`
Multiple accounts	I am NOT logged into multiple accounts
Browsers	Tested on latest versions f 5 major browsers
Copy script	When I make a copy of the script, I get the same result as above
Tested on	The above applies to my google.com and my legacy free GSuite account. Tested also in incognito mode. Tested by logging into google account that got edit access to the spreadsheet then script editor was opened from the spreadsheet and /dev access from the editor
Copy spreadsheet	When I make a copy of the original spreadsheet I am able to access `/dev`

I have a web GAS project that was working in production for months. Now there was reported an error by a user of the actual application. I went to investigate it and wanted to open test deployment but received

"Sorry, unable to open the file at present."

"unable to open the file" error screenshot

Details

The project is bound to a Google Spreadsheet. I am not the owner of the Google Spreadsheet that GAS code is attached to. I never was.

Troubleshooting steps I've taken:

I tested the issue on Firefox, Edge, Vivaldi, and Chrome. The latest version of the browsers and restarted my computer. I was able to reproduce the issue on both Gmail account and legacy GSuite account. I am not logged into multiple Google accounts. Gmail account returns this dev URL: https://script.google.com/macros/s/<deploymentId>/dev. GSuite account returns this dev URL: https://script.google.com/a/macros/<domain>/s/<deploymentId>/dev

I created a copy of the Google Script and modify it so it can access the original spreadsheet. When deploying I got this error message

"Only users in the same domain as the script may deploy this script."

I am not the owner of the new script. My role is editor. I am not able to deploy under my GSuite account. The owner is on Gmail. I am able to create new deployment under my Gmail account, but I am not able to access test environment:

deployment error screenshot

The script owner has the same /dev URL as I do and is getting the same error.

The question is self sufficient, but I made short video to show that /dev(test environment) end point is not accessible and throws this error, but versioned deployment(/exec) is accessible.