As reported in the Spanish Wikipedia, and also an issue I got when translating some pages, those pages are locked, with no chance to make it and save to the user's Sandbox. The idea here es allowing the user to use the tool even if the translation was already done by other user, allowing to publish in the user's sandbox, but disallowing to publish to the page to the mainspace.
This is a limitation of the tool that we plan to solve in T86151: Allow different users to translate the same topic independently.
Since this requires a significant change in the data models, we'll focus on it only after completing the work on the next version of Content Translation.
Meanwhile, we are working towards automatically removing old translation drafts in T183890: Remove very old translation drafts from CX database. This won't solve the core issue, but would alleviate some of the consequences.