If this is only happening with DXD (PCM 352.8 kHz) or DSD64+, this is a known issue, I have had it myself. This is a bug in the latest official firmware update 3.0.137 that KEF issued April 26, 2026. You can find other threads on the matter on this forum.
You can/should report the problem to KEF via the KEF Connect app („report an issue"). In my case, they came back early July with a new firmware (3.0.138) which is not officially distributed, yet. I supplied them the MAC address(es) of my LSX II, and the firmware was updated. Roon running smoothly again, since.