First off, I wanted to thank all the programmers who made Stella 6 on the Retron 77 possible! I actually purchased it once I saw that the old Stella 3 emulator had been updated, and am very happy with it, all thanks to your hard work!
I updated my Retron 77 from Beta2 to RC1 by way of overwriting the uimage, and ran into a strange issue. If the TV mode in the Basic Settings window is switched from RGB to Composite, it seems to break the phosphor blend and games that make use of flickering will end up "losing" sprites. This is most noticeable in Pac-Man, when 2 of the four ghosts disappear. Going into the menu screen and switching to Disabled will rectify this issue. I thought at first that it was due to me just updating via uimage, so I reimaged my SD card with a clean image, and did not change any settings save the TV mode. After playing Pac-Man for a bit, the issue returned. Note that I did not run into this issue using Beta2.
I am happy to try different things or collect additional details, if it would help determine what is causing the issue (assuming that it IS an issue, and not a byproduct of the updates/improvements that are being made).