iMac 2015 why does the ethernet connection disappear for a few seconds?

Question

iMac

Hello!
I have iMac 2017 late 2015 i7. last axle.
The Internet is connected via wire to the time capsule. Periodically, the computer loses its IP address and it takes up to half a minute to get a new one from the router. Why is this happening? How to get rid of it?
There is no such thing on wi-fi, but I can’t use wi-fi, there are too many neighbor networks, everything is noisy.
There is also a Macbook pro 2016, also connected via wire and does not experience such problems.
Tell me how to deal with this?