The are a lot of messages with a heal including every node sending a message to every other node to find its neighbors. If you are not moving around the devices and have Zwave+ devices it has little value. Frankly, I never use it.
The other culprit could be several chatty nodes that are sending messages every few ms, electric meters can be bad actors.
As noted above using debug and viewer will find the (or at least point to likely) problems.
Older post but still informational. [SOLVED] Unresponsive Z-Wave Network: Tools and Approaches to track down the issues - Tutorials & Examples / Solutions - openHAB Community