Hi @IN, thanks for taking the time to report this! Unfortunately this Wikimedia Phabricator task lacks some information.
If you have time and can still reproduce the situation: Please add a more complete description to this task. That should be

• a clear and complete list of exact steps to reproduce the situation, step by step, so that nobody needs to guess or interpret how you performed each step,
• what happens after performing these steps to reproduce,
• what you expected to happen instead,
• a full link to a web address where the issue can be seen.

You can edit the task description by clicking Edit Task. Ideally, a good description should allow any other person to follow these steps (without having to interpret steps) and see the same results. Problems that others can reproduce can get fixed faster. Thanks again!

https://w.wiki/vqd (mobble)

I'm unfortunately not sure how to interpret this... Do you go to https://en.m.wikipedia.org/wiki/User:Lickmeinsideout27/sandbox (non-mobile URL)?
Did you mean https://en.m.wikipedia.org/wiki/User:Lickmeinsideout27/sandbox (mobile URL because .m., but not where your link above brings me)?

Could you please post full URLs instead of shortened/obfuscated links, if that's possible? Might make things a bit clearer for readers of bug reports...

You can see editnotice that appear in the desktop view are gone on the mobile side.

Where exactly to see some edit notice in the desktop view on https://zh.wikipedia.org/wiki/2019冠狀病毒病香港疫情 ?
How is this related to "leaving a message to a user" mentioned in the task title?
Could you please follow https://www.mediawiki.org/wiki/How_to_report_a_bug and provide a complete list of clear steps to reproduce, step by step, as a list, plus what you expect, and what happens instead? Following that scheme usually helps reducing misunderstandings or different interpretations. Thanks a lot! :)