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Please elaborate the question with more details: if the cpt is edited and replushed, it defaults the '&' back to code, and then it doesn't show up in the front end search.
What code does the '&' back to?
I have tried it in my localhost, with below steps:
1) Create a new post, post title is: at&t
2) Save and edit, save above post again, there isn't the problem you mentioned above.
So the problem you mentioned above is abnormal, please check these:
In case it is a compatibility problem, please deactivate all other plugins, and switch to wordpress default theme 2019, and test again