Just a thought - have you tested to see whether the version which the client sent back for you to change worked?
If you are issung development versions to the client, it is possible that someone has inadvertently changed something prior to you getting it, so looking for a solution in your latest work may not be the correct place to start. This is probably a long-shot and you may very well have checked but I thought it worth suggesting - there is an element of "experience" in this suggestion ;-)
I would start by putting breakpoints on every bit of code I thought was relevant to the opening/loading/refreshing of these forms. I would then be stepping through all the code making sure it is doing what I expected. Perhaps certain events aren't firing in the sequence you think, or perhaps there has been a database change which is causing your refresh query to fail, ... the list goes on
Another one which comes to mind (again an element of experience) is - are you building and executing a query in your VBA? If you are, use a breakpoint and the Immediate window to capture the sql created and test that.
Other things to check are changes to control or form names, or maybe form referencing.
If none of this helps, I think what would be useful is information on how you have linked the subform to the master and maybe even the code of the right-click event along with any other subs or functions called from it.
Once you get this solved - and you will - I would suggest making sure that for live usage, you compile the front end eliminating any future uncertainty.
I have spent many frustrating hours debugging subforms and functionality driven from them - I hope some of the suggestions above lead you to a solutiion.