Having installed several other games that appeat in the Connect section without issue, I beleive this problem is with the Diablo 4 game not integrating properly.  

Hello, I have a similar issue with Razer and Diablo IV. I have a Corsair K70 keyboard, and I recently purchased a Razer Basilisk V3 Pro. I had no problems with iCUE while playing Diablo IV; the keyboard's RGB lighting worked perfectly. I installed Synapse 3 and other Razer modules to try it out (I'm new to Razer), but the Synapse software didn't integrate properly with Diablo IV. Other applications work without any issues, such as Opera GX (which I use to test RGB synchronization with two different programs, iCUE and Chroma), and synchronization works fine on two devices with both iCUE and Synapse running simultaneously.

I tried closing iCUE before launching Diablo IV, and then the mouse's RGB lighting functions correctly, and the game takes control of the RGB lighting. When I close Diablo IV, the RGB control switches to Razer Axon (I can see on the second screen that Synapse detects the applications without any problems when iCUE is not running). However, when Corsair's software is running, iCUE detects the Diablo IV game, and the keyboard works, but nothing happens with Razer's Synapse software; it doesn't detect the game.

Could this be some kind of software incompatibility? I attempted to reinstall all Razer modules, but nothing changed. When iCUE is running, the game is not detected as running in Synapse 3.

I tried the "Chroma Control" application to see other RGB devices in Synapse; the Corsair keyboard appears in Synapse, but nothing changes because this application requires iCUE to be running to control the Corsair keyboard.

I'm a bit frustrated with my Razer mouse because of this issue, and I'm considering returning it, even though it's a hardware marvel. The software experience has been disappointing. The only app I managed to get both devices working with is SignalRGB, but I don't understand how a third-party application can make everything work smoothly when the manufacturers themselves can't seem to implement a functional application.

There is definitely a problem between Diablo IV and Razer synapse.  I have been using my Naga Chroma which is my go to mouse for rpgs and it has been getting more and more difficult to get the game to react to my mouse.  By that I mean that if the button number is too high > 6 the game does not respond which makes it impossible for an old fella with fat fingers who spreads the four available functions around the mouse buttons for accuracy.

I note there have been several other problems with Synapse and Diablo 4, has anyone at razer looked into this, cos right now its preventing me from enjoying the game.

I checked to make sure that all buttons were recognised outside the game and they were, so I cannot conceive of any explanation other than incompatibility between the two pieces of software.

Any news on this? Diablo 4 was working for me last week then suddenly disappeared? Annoying as it was really cool when taking massive damage, my whole room would flash red