Kansei Ben Kissi Kissi
Yeah, one single slip up (forgetting his voice changer under the pillow), let to lots of trouble.
Not only that speaking Kansai Ben was highly suspicious (specially when only a few hours later the gang meets "Mr. Kansai Ben, Shinichi's Best Pal" Heiji Hattori himself.), but then saying "It was my voice, but it wasn't me!"
And then, Masumi starts poking in the wound by mentioning that Shinichi folded his sleeves like a little kid would do. Heck, he can really be glad that Ran started talking about the movie poster.
(The Red Thread people actually think that she might have done this on purpose. Personally I'm not sure about this.)
Ah Le Le
Ok, Shinichi, you have really been Conan far too long. Seriously, changing into "Conan Mode" RIGHT IN FRONT OF RAN AND CO.?
And then look at their faces.
Sonoko: Annoyed. Masumi: Smirking. Ran: Worried (?)
While it wasn't the first time, that Shinichi slipped up when he was himself again (Calling Ran , "Ran Nee Chan" once, during the Desperate Revivval), this time it was almost as if he's holding up a big sign in front of him with "Hello, I was Conan Edogawa all the time".
Heck, it's actually the first major time, that Ran has indications, that Shinichi is Conan and not visa versa as usual. ("Sleeves, Ah Le Le")
And in conclusion, with the Red Thread Observations in the OP, which Gadgets of Conan Ran is currently aware of, he now might have accidently revealed the indentiy of the Voice Changer to her. (She she might have suspected to exist anyway, if she's really in suspicion mode again.)
Plus: We know Gosho love of planting hints in-universe and out-universe. Things are clearly getting fun again..^^