Update: This bug was fixed with the 4/2/2021 update.
When updates are made to the Custom Text in OE Admin, many users open the Admin settings and Parent Portal to see the current English text while they work on the translations. However, Multi-tab browsing with custom text in another Language and English overwrites all English because the last page rendered was English. To avoid this use the 'Show English' to view the text to translate.
Additionally, make sure you are working on the correct Language page.
Saving the Custom Text sections individually should also help to avoid any problems
We are aware of this issue and an Idea has been created to follow the progress. https://ideas.aeries.com/forums/265851/suggestions/40951474