Yesterday was really cruddy, I spent over 8 hours in two Vocaloid Discords trying to figure out a solution on how to get the Meikas to sing. There were only about 2 people that got them to work (one right away, one after moving their files and reinstalling). I saw at least 6 people (including me) not able to hear sound from them, we reinstalled their voices, reinstalled VOCALOID5 Editor, compared settings and methods, but nothing was working. Someone on the VocaVerse Discord who couldn't hear them sing got them to work in the 4.5 Editor and finally in VOCALOID5 Editor after purchasing them.
I even wrote to Gynoid and they replied twice, once to say it might be an audio driver issue, another time saying they weren't providing support with the demo.
But this morning, it seems to have randomly begun working for people (including me). If you had issues hearing them sing, try opening the editor and check it if they are finally working. Also, I heard on Twitter that something goes wrong with their trial if you try to import a MIDI, but I haven't tried it out.
Personally, I'm NOT happy with this sloppy demo business and I feel like I can't defend VOCALOID5 Editor anymore with its update issues, high cost, lack of demos, forcing people to buy at least 4 Vocaloids they might not want, slow software, etc. : /