A swimming llama that touches water plants will spin rapidly in place, which stops it from following a caravan. This appears to happen for plants that grow in or into the water block with air above it. Plants that haven't reached the surface water block don't appear to be a problem.
Environment
Ubuntu 18.04.2 64-bit with Java 1.8.0_172 64-bit connecting to Vanilla 1.14.1 server.
Duplicate of MC-136318