As far as I’m aware, the only way to solve that is
- remove all of the envelope points,
- save the project,
- update to Audacity 3.0.4 (which has a fix for this bug),
- open the saved project in Audacity 3.0.4
- remake the envelopes.
To remove all of the envelope points, run this code in the Nyquist Prompt (https://manual.audacityteam.org/man/nyquist_prompt.html)
;type tool
(aud-do "SelectAll:")
(aud-do "SetEnvelope: Delete=1")
"Done"