There is no such thing as “re-encrypion” or “while decrypted”. Decrypted data is never written to disk. Data is decrypted on the fly when it's loaded from the encrypted disk, and encrypted on the fly when it's written to the encrypted disk.
When you enter your encryption password or insert the smartcard with the key, the system doesn't instantly decrypt all your data. What happens is that the system loads the key into memory (or unlocks the key if the key is resident in a secure enclave such as a TPM).
Therefore a crash does not leave any unencrypted data on the disk.
A crash, or even a normal shutdown, can leave unencrypted data in RAM. RAM contents become unreadable quickly after the RAM loses power, but not instantly: it takes a few seconds. Of course, having the computer stolen while powered on carries the same risk. So it's all part of the same concern: having the computer stolen while powered on or while being shut down.