Revise LINQ usage of `Any` followed by `Single`

[Youssef1313]

Why not simply Where to collect all potential duplicates (although we should not have any).

Originally posted by @Evangelink in #5717 (comment)

[Youssef1313]

I am never a big fan of Single API because when it throws it's hard to debug, you don't know what was there.

Originally posted by @Evangelink in #5717 (comment)