Proxy issue 404 error for root path

[Denys-Sokolov]

Setup Proxy: https://shop.com/track-trace 
Subpath prefix: tools
Subpath: order

Example #1 (with path any-value)
https://shop.myshopify.com/tools/order/any-value -> https://shop.com/track-trace/any-value  - OK

Example #2 (w/o any-value path, try a root of proxy)

https://shop.myshopify.com/tools/order -> https://shop.com/track-trace - 404 Error

Redirected to https://shop.myshopify.com/tools/track-trace?shop=shop.myshopify.com&path_prefix=%2Ftools%2Forder&ti...{...}

https://shop.com/track-trace working, return 200 code
https://shop.com/track-trace/any-value working, return 200 code

Do you have any ideas?

BTW if use proxy w/o path - Examples #1 & #2 are OK!

Setup Proxy: https://shop.com