Maybe if the languages are very similar. If you convert C to Rust using AI it might work well but will most definitely not leverage the unique features of Rust. Might as well stay with C in that case. Migrating from an object oriented language like C++ to a language with another paradigm (such as Rust) will most likely produce a burning pile of shit

Easy to achieve if the ai just wraps all code in an unsafe block ^^

Also, Nextcloud/Owncloud are written in PHP, that might also have a significant impact on its poor reliability ^^