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Many RIA owners also report changing magazines to something else (like Wilson 47s) fixes many feed problems. I'd try that before anything else.
(RIA Tactical owner here).
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+1 on both checking the extractor, and on RIA magazine quirks.
While my RIA would work fine with the ACT-Mag that it came with, it wouldn't lock back on empty with any other mag at all. All magazines other than the one ACT mag, the followers would ride up past & around the slide stop; so not only did the slide not lock back, it bound up the works when trying to remove the magazine (since the follower was on top of the RIA slide stop instead of under it, and had to be forced down around it to get the magazine out).
I changed out the slide stop, and now it works fine with every magazine I've put in it since; including the ACT-Mag that it came with.