Thus far I have only seen reports of this in 2021 when saving a scene. Perhaps whatever change resulted in this old issue coming back might have been back ported to 2020.3.
Are you having text objects disappear when saving a scene or at runtime? If runtime, this is likely the result of having multiple text objects that share the same material preset but being rendered in a mixture of rendering space like Screenspace, Worldspace and Overlay. The solution for that is to use a separate set of material preset for these different spaces. There should be several detailed posts about this on the forum.