This is defined priority Normal, instead of High, as it is not a new issue, however, it has only recently been noticed by users, identified by developers, and with a replacement available.

The issue is that even though the legacy set and loadFile functions call the same validation check function, it is only successfully called in the former case, leading to commit errors in the latter case; commit errors will result in an absent config section in the resulting loaded config. The root cause is being investigated in the legacy code, but the immediate resolution is to replace the legacy loadFile now, with one of several alternatives. It would appear now that the discrepancy in performance between legacy loadFile and explicit (using batch set commands: T5815) or implicit (using CStore adapter: T5528) replacements is partly due to the legacy function calling incomplete validation instances in its validation calls.