file system - Why is TRIM not supported on encrypted "/data" partition?

I have a rooted Lenovo A369i. I use LagFix (fstrim) to TRIM partitions. Previously it was working well with /data but after I encrypted my phone it doesn't. I decrypted my phone by formatting. But now in the app it shows /data partition having kernel or hardware issues. It's not hardware because before encryption it was working well.