I've noticed that every time my game has crashed, all my advancements that I achieved are no longer there, and I have to get them again. e.g. I have slept in a bed in this world many times, and have completed the sweet dreams advancement, but when I sleep in a bed in that same world for the first time after my game crashed, I will get the sweet dreams advancement again. This is the same for all the other advancements. This bug has been around for a while and is still an issue in 1.16.
Related issues
Comments

Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-187701, which is a report that has not been resolved yet.
If you want, you can upvote the parent ticket, and enable watching to receive any updates about it - if you believe you have any information that may be important for this issue, please leave a comment on the parent. Please also use the search function in the future to prevent duplicate reports.
Quick Links:
📓 Issue Guidelines – 🛠 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki
💬 Mojira Subreddit – 💬 Mojira Discord