While watching HDR HLG content on YouTube via Toshiba 55U7950 certain things looking like this massive red ball and totally losing the detail... Is it a known bug?

by VladimirUK
Istarica

I have to say mine isn't as bad as yours. But it's indeed less detail than SDR version.

https://imgur.com/a/PPlPd9x

GbMaxSE

YouTube doesn't support HLG.

VladimirUK

This issue was fixed by firmware update !

ExcitingCommand

Glad to hear your issue fixed by Toshiba support firmware.