I was facing the same issue, this is because the date format is incomplete, nifi is expecting the milliseconds too, like this

2024-03-27 00:00:00.000

i.e.

yyyy-MM-dd HH:mm:ss.SSS

After using this format, NiFi stopped throwing error.

Refer to this link for detailed explanation : https://community.cloudera.com/t5/Support-Questions/value-cannot-be-converted-to-a-timestamp/m-p/382750/highlight/true#M244681