Yes, it happens on the new APFS format for me.
This has been discussed so many times, that simple google/macrumors search would answer this.
APFS format does not release space on delete:
1. APFS can have multiple pointers to one data record, if it is used by multiple files. For example, if you duplicate a file, no new space is used, APFS simply creates link to the existing data. Logically, deleting that file (link) from one place makes no difference in space used. Only deleting the last place the data is used gets the data really deleted...
May be - may be not :
2.If you are using Time Machine, TM keeps data for about 24 hours locally as short term TM backup - and so it can back them up when disk is attached later. This is the hidden space... There are instructions on line (try google) how to prune the tmutils space they are using manually.
Somehow surprisingly, it does same when you are not using TM. In any case, the space was marked "purgeable" and if needed, should be automatically released to OS.
It is confusing and works well ONLY if you have large amount of space on drive - basically, when you do not care. I have about 50% of space available all the time on my 1TB SSD and all of the above behavior is generally transparent and works really, really well.
Since Apple is still selling Airs with SSD of 128Gb, there must be lots of confused users desperate for space on their systems.
Unless you get in troubles (with 350GB I doubt it), ignore and live your life. It's not worth fighting with it, usually it works.