Ghost type are not guaranteed to escape from wild battles and im pretty sure they are not immune to mean look.
its pretty anoying when my level 85 max speed Shedinja is locked into fight with a level 30 Raticate that uses sucker punch and kills my pokemon instantly.

Escaping with higher speed also might be glitched. only taking into account base stats, Because ive been locked into battle with level 5 Rattatas with my level 80 max speed Shedinja and its also pretty anoying.

Generation VI onwards
Ghost-type Pokémon are now immune to effects that prevent recall or escape (such as Mean Look and Shadow Tag), and they are also guaranteed to flee from any wild battle regardless of Speed.

I'm not too familiar with the mechanics here, but I'll pass it along to people who understand that better. Keep an eye on the ticket!

Yep, I was reported this a while ago, it was tested, but closed. After recent retests, it showed that Gengar was not able to run from an Arceus battle. I haven't tested Mean Look, but I've been told that apparently shadow tag works? If you want to double check that. Anyway, fix upcoming.

Just had a look at the escape issue, but I cannot reproduce that. With a level 80 Shedinja with 31 speed IV and 252 speed EV I can flee from a level 5 Rattata every single time. Are there any specific steps I could try for reproducing that? Any held items?

the level 80 shedinja thing not being able to escape doesent really have any reproducable steps its just kinda random i would say i get away about 80% of the time. i might be wrong with my ev's/stats or something shedinjas speed is pretty low naturally though but im pretty sure i outspeed a lot of this stuff i get locked into battle with.

Should be fixed in 6.3! Thanks again for the report.