as I’m experiencing the same problem, but I likely have a different root cause (I only started using Z-wave in the binding 2.5 era), I found this topic and I think I can take a thing or 2 from it in my own research. Since the indicated solution in this post [SOLVED] Zwave Network very slow or not working after Update to 2.5 is merely a workaround as a solution,
I would like to share with you the following:
My Aeotec Z-Stick Gen5 became slow a week after I added 2 floordimmers from Idinio, https://www.shada.nl/products/5296/idinio-z-wave-50w-led-foot-dimmer. As the inclusion was not as smooth as any other product I added, I have my suspicion, but nothing to back it up so far.
3 days ago I decided to create an rule to animate the light connected to one of these floordimmers since the kids had decorated the bulb with a Christmas star. The rule made the lamp flash 10 times with 0,5s interval every 20 min. The problems started the next day: Some commands are delayed, others are lost and the entire zwave network is affected, which leads me to the Gen5 stick, as the wifi devices are holding strong.
Also Aeotec mentions the symptom on their support pages: