Hello, While other users of Kantata might chime in, for narrowing down the problem I'd recommend you begin troubleshooting using the guidance here https://learn.microsoft.com/en-us/defender-cloud-apps/troubleshooting-proxy#more-considerations-for-network-conditions. From the MCAS/MDA Cloud App Catalog, I see their DC is US Based.
It would also be helpful to know what the perf degradation looks like (e.g. is it a sign-in/when browsing/downloading), and what are the related MCAS/MDA CaaC policies applied on the app.