Why can't I see a folder in "/storage/emulated/0" on PC through MTP?
It seems to be a problem related to Media Providers. Due to some bugs in implementation of MTP, database of Media Storage app (/data/data/com.android.providers.media/databases/external.db) built from contents of /storage/emulated/0 isn't updated or is delayed or isn't properly communicated with the client as the files change, so MTP shows outdated / incomplete contents.

In order to force database updation, delete the file and run some media scanner app. Non-root users can delete this file by clearing data of Media Storage app.
But be aware, it'll also clear internal.db which will make ringtones unavailable and a new database will be built from /system/media on next reboot.

See this answer for more details.