Players are reporting massive problems with Red Dead Redemption 2 and especially on the online version of the game, Red Dead Online recently available in beta version on PS4 and Xbox One. It is the PS4 players who are affected by this error whether it is on standard PS4 or the Pro version.
The CE-34878-0 error is well known to the PlayStation community since it has been going on for several years without explanation from Sony… For the Red Dead Redemption 2 case, and in particular Red Dead Online, it must be an internal problem of the game and not of the console. If you have crashes with a return to the menu and error message CE-34878-0, you just have to restart the game and hope not to be affected by this bug again….
The crash is without consequence for your machine, although we grant you that it is annoying. It will certainly be necessary to wait until the beta phase ends and Rockstar Games teams deploy a patch to correct this internal concern in Red Dead Online.