SSRS 2016 - cannot see parameter
SSDT/Visual studio is strange and strange glitches such as this occur quite often. Another similar glitch is when changing the dataset sql query, sometimes you will have to delete reportname.rdl.data in the project folder for the changes to occur.
Saving and reopening is the only guaranteed way to fix your problem.
I have seen the same issue. You don't even need to close and reload the project or VS 2015 (SSDT), you can simply close and reopen the report and then the parameters should display fine. I haven't been able to always reproduce this, maybe it is when a parameter is added because I just had this happen to me again. Definitely a bug that needs to be filed.
Save and close VS. Reopen the project OR Unload and Re-load your Reports Project.
The parameters will now appear!
I had this same problem. Super frustrating.