The skeleton itself is a “feature”. We show it when messages are not yet loaded to improve the experience of scrolling.
I think what you’re pointing out here is that there is an unexplained and/or unexpected performance difference in loading earlier messages when in the drawer mode, and your evidence of that is that the skeleton appears.
I think skeleton should only be active on initial load when you open a channel. The commit I linked above contains this on description “show skeleton only on initial load” which works fine on full page chat desktop and mobile. Only drawer keeps skeleton for this purpose and this is why I think this is not by design.
Now it uses always when you click to show a reply or a link to a previous message in the same channel even if the message is loaded. Here is an example the replied message is already loaded.