It is, when Seika has joined you it will take Ayane's position, not letting Ayane to be able to return. Sorry, the only fix is to not let Ayane be deployed when Seika becomes available for deployment.
Okay so I haven't deployed her but when I deployed seika I get an error. And when I continue to ignore the error it brings me to the main menu. So, I'm not really sure what to do with deployments.
Nah I know how hard it is coding. It can be the smallest thing that you skip over without realising but cause crashing bugs, that'd why I stopped. So it's all good.