I’ve been seeing this issue of not all modules being detected with the community/HA-maintained add-on come up on this forum relatively frequently. Unfortunately, it also has been a pretty long-standing problem at this point, and it does not look like it is getting addressed (not sure if its because doing so is difficult or just because the maintainers of the addon solved their problems and don’t actively contribute to the addon anymore.)
A relevant thread to read through for some more details is at Velbus Home Assistant missing module instances. Here’s another: Home Assistant does not find all my modules. There are also some relevant-looking issues in the repository by @cereal’s velbus-aio library that this integration is using: Velbus in Home Assistant not detecting all modules · Issue #118 · cereal2nd/velbus-aio · GitHub.
As you can gleam from these references the reasons can be multifaceted: anything from the way scanning is implemented to possibly limited support of certain modules, especially the newer ones.
Another reason why H-A side of things should be suspected is that usually people report not having similar problems with the other ecosystems in their systems. OpenHAB is known to have a very stable Velbus support, there are people integrating velbus into their NodeRED workflows with no issues either. I’m not sure if anybody is using Velbus in some of the more obscure home automation systems, but in my time lurking around this forum, I haven’t heard any relevant complaints about those either.
That said, I have some suggestions of things to try and bits of knowledge that may be useful.
It is important to understand that this delay is almost definitely not on the part of the Velbus bus itself. If the message ends up on the bus, modules will react to it pretty promptly (like, up-to 1ms range.) The only reason why components (e.g. signum or a VMBUSB*) might hold off on sending a message out to the bus is if the bus itself is already very contended, but in that case you would also see a similar delay when operating the velbus system by pressing buttons on your panels. Which doesn’t sound like an issue you have.
That means the delay you’re seeing is introduced by the components leading up to your connection to the Velbus bus. There are some tools that can help you to diagnose where the delay might be occurring, but they might not be particularly friendly to people not used to administering UNIX systems or just those without some networking knowledge. An example of such tooling would be tcpdump or wireshark which would allow you to inspect the network messages between H-A and Signum or Velserv. I believe wireshark should be able to also inspect USB/serial port traffic, so you’d be able to see when the message gets sent out to the bus when connected over USB. Finally a good place to look at might be some logs from H-A itself (ref).
Is more likely than not closely related to the delayed operation when operating velbus from H-A. Module scanning in Velbus relies on timing of responses: if a response to a module “ping” is not received within a couple hundred milliseconds, the address (and thus the module) is generally considered unused. This is how module scanning works in all velbus integrations, including Velbus Link. In principle if there are no communication timing issues introduced somewhere along the line, all scanning implementations should work roughly similarly. If putting said ping on the bus takes a full second in the first place, then it is quite natural that the response to the ping won’t be back within couple hundred ms.
A big benefit of Velbus Link here is that it also has a bus log that you can monitor to see what’s going on in terms of bus communication. So for example when you say that HA is not able to discover anything at all, when connecting over USB or velserv, velbuslink connected to the bus at the same time is a great way to check if the module scanning messages are making it onto the link at all. This can be much more approachable than wireshark or similar tools I mentioned above. If you end up not seeing anything in the Velbus Link communication logs, then its a great indicator to check if your connection configuration is correct at all.