XU4 negotiated ethernet speed goes down

Hello everyone, I have an XU4 that I use as a webserver and I noticed that after a while the connection with my switch goes to 100Mbps and then disconnecting and reconnecting the ethernet cable it renegotiates to 1Gbps. Having a 200Mbs WAN connection, I need it to stay connected at 1Gbps, for internal traffic as well. What can I do to solve the problem?

I’ve also posted on Github: https://github.com/MichaIng/DietPi/issues/5066

Keeping discussion on GitHub now, hence I’m locking this topic to avoid splitting conversation.