So, to recap.
the issue is not present if tessellation is off, but when enabled, it flickers despite a bounds extention in all directions and a near clip plane value of 3.0?
Can you extract the level from the project (move to a new project), delete everything except the tiles with their material, and package it for sharing? (Not package as in publish, but just copy/zip the project. The settings are needed as well).
With that, you can either share here for anyone to check, or share directly with Epic in a bug report.
I can’t say I’m able to replicate this behaviour however, so it must be a combination of settings (and maybe when you move it to a new project the issue may disappear).