It is useless to report such graphics glitches for v1.26.9 (I even clearly said they existed, in both the release notes and the thread on the material viewer): they do exist and will be fixed as progresses are done on
viewer-development-material.
Instead, you could report the graphics glitches in the JIRA, under the MATBUG tag, but it'd be better to report them while referring to LL's own project viewer to avoid suspicions by LL about a bug in my own backport. Be aware that LL's current project Material viewer lags a full week behind the latest shader changes and render pipeline, so better waiting for LL's next release before reporting these glitches.