Does anybody know why this happens or a solution to this problem?

I've been running Windows 10 since February but I believe it happened with 8 as well.

Any help is greatly appreciated.

Can you see the default maps as well or is the map selection list completely empty?

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Wow sorry I didn't expect anyone to be active, never-the-less an almost instantaneous reply.

Yes in the folder aside from the maps I'm trying to install, any of the folders I can find, it's empty. If this helps I go through Origin with the Ultimate Collection.

I'm having the same problem
Win 10 + Origin + Ultimate Collection = Only standard maps show up in skirmish.
(I was going to review some RA3 maps and then this. I guess I'll use steam for this (Don't actually know if this will work, I'll get back to you on that).)

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Check all waypoints.. ie : Player Start Point..

Once i have problem .. i delete player1 start point and the map didn't show @ skirmish..
after i fix & check all player start point .. it fixed