Each version has a corruption limit. For example Hos.138 public its Kelly 1900 max. Ash 600 max. Viki 600 max. Steve 250 max.
Viewing post in Stuck at Level 2 Corrupt 1700
Could also that there are not updated scenes in game.
for example when kelly peeps viki in pe, this makes here down again to 400 (in 1.38)if i avoid this scene i can level viki to 600, so perhaps you look, what you use to corrupt kelly, there could be a scene limited to 1700 and each time you trigger this scene Kelly goes down.