This may be totally bogus, but for all my report generation sequences in Method the first Action that I have in the sequence is a Save. I also save again at the end since I update Invoices with the print date when the print Invoice button is pressed. The report generation all happens on the Method server, I believe, but I just want to make sure that all the browser information is fresh updated to the server.
I looked at your problem since at first I thought you might be talking about another pdf problem where a pdf attachment to a record won't open. Which is also fixed by reselecting the record in question. For example if you have a screen open that has a pdf attachment on another tab and you switch to that tab, often you get a 404 resource not found. But if you reselect the record and reload it on that tab, the attachment will load.
It's not easy to keep browswer contents truly synch'd with the server reliably and not sacrifice performance. I don't really know how to effect these kinds of cache refreshes programatically in Action Sequences and for the most part the Method code is really good about this, but sometimes I throw in something I think will force a reload of form or screen data just in case.
I do the same stuff when trying to automate grids. Sometimes I throw in a full Save action just for good measure since some of the grid row or grid saves are not complete.
Again, all the above may be totally bogus as I haven't regression tested some of this stuff, just hacked up some fixes some time ago.