So, from what I can see, the log is serialized fine (it's just that it's done old style, and not in its own file). The problem has more to do with the fact that it's just not possible to unserialize the job macro status because of https://github.com/xwiki-contrib/macro-job/blob/7e52f5268a659034f4969aec2c971b39005e41b7/macro-job/src/main/java/org/xwiki/contrib/jobmacro/internal/JobMacroStatusWrapper.java#L98. So not sure this ever worked.
