Hi @YashPi,
I understand, this is frustrating, and the workaround of duplicating templates is inefficient. Here’s few reasons which you could validate in your environment.
1. Clear the local cache
2. Make sure multiple users are not working on same template at same time, there could be concurrency issues where the changes aren't properly saved or overwritten.
3. Is your HTML template complex? Is it possible to simplify it?
4. If nothing helps, and environment is Adobe managed, contact Adobe support.
Thanks,
Jyoti