Odin Inspector prior to version 3.0 can trigger a degradation of domain reload times and slow domain load times in Unity 2019.4 and above. We've contacted the developers and reported the issues that we discovered. Some of these issues are already fixed in their current 3.0 beta.

If you're using Odin Inspector and are experiencing slow or degraded domain reload times, it might be worth a try to check out version 3.0 if possible.