Best guess is the transmission fluid was ignored for a period of time and that allowed varnish to build up on internal components (shift valves, etc.) which makes them sticky and causes late or missed shifts. You don't say what your fluid change method was, whether a single drain/fill, multi drain/fill, or if you disconnected cooler lines to cycle in completely new fluid. The transmission capacity is about 8.3 qts and a single drain/fill replaces about 3.3 qts of that. The theory on new fluid in a varnished up trans is that larger chunks of varnish break loose and cause these random/sometimes more frequent late or missed shifts. When dealing with an ignored transmission it is generally recommended to do multiple drain/fills driving several thousand miles between each one to let the new additives in the fluid work slowly rather than aggressively. It sounds like you ended up with the latter. Many shops refuse to service high mileage transmissions with fluid that is in really poor condition for exactly the issue you have encountered because the customer returns to the shop insisting that they "ruined" their transmission when the damage was already done.
There are two ways to proceed from here. Either a complete tear down and rebuild cleaning all these components in the process, or if you are in a position to baby it while letting the additives in the new fluid continue to work on cleaning the troubled components it may over time works it's way out of it. Honda is very adamant about not flushing their transmissions, but IMO that would be on table to try with the understanding that you may be facing a rebuild anyway and giving it a good chemical flush may save you that trouble and if it doesn't you proceed with the rebuild anyway.
2007 MDX Tech Billet Silver
2007 Honda Odyssey EX-L Nav/Res
30+ Years Automotive & Related Industry Experience