Every team I've worked on that has switched from Kanban to Scrum has slowed down and never regained the previous velocity. Further, many of the promised benefits of Scrum (things like better insight and predictability about delivery rates) never materialized. Every team that I've worked on that has switched from Scrum to Kanban saw an immediate improvement in speed that never disappeared. Once, just once, I was lucky…
However, Scrum doesn't make much sense if you don't continuously iterate. Another symptom of this is people measuring velocity instead of value created. To properly implement Scrum, you actually need to measure the impact of the work completed in the past two weeks. Unfortunately, most teams don't do this, instead they focus on measuring velocity since it's easier and within their control. It's worth noting that it's completely fine for teams not to constantly iterate and change direction (including high-performing teams), and in those cases, Scrum simply isn't the best tool for the job imo.
I must admit that I personally prefer Kanban for almost all workloads.