I have the updated version and am still experiencing this problem. After being frustrated and trying everything to fix it on photoshop I FINALLY got something to work. So what worked for me was going to my render settings in after effects and changing my format to "PNG sequence" and channels to "RGB+Alpha" (for transparent backgrounds) then under my save settings when I export I click the check to save in subfolder and named it (because its gonna be a bunch of still image files and you don't want those floating around everywhere) then when I open it in photoshop I just selected one of the still image files and the checkbox for "image sequence" which open it up like normal in photoshop with a timeline. After that my export -> save for web settings worked like normal and I was able to export it as a gif without the error pop up.
hopefully, this works for everyone else here too but I almost cried tears of joy when I figured this out, maybe photoshop was having trouble because it was previously a video file idk