This is from issue 02010202.
With the previous web interface (up until verrsion 15.5.1) the process of creating a shareing link also included as (I think step 3) to directly upload files which are to be shared. Only when this was done did the link get created and the invitation mail got sent.
With the new web GUI uploading files is an extra step which has to be taken after the link is created. Would be neat if the files could be uploaded again during creating the link.