In the most recent beta, the composter got a fix for this. Should be easy to do the same to the cauldron, looks like it was the same issue.
MCPE-43195
Cauldrons' lighting is wrong
Resolved
Duplicate
1
(Unassigned)
Unconfirmed
Windows
Windows 10
1.13.0.1 Beta, 1.12.0.14 Beta, 1.12.0.2 Beta, 1.11.0.10 Beta, 1.9.0, ..., 1.11.0, 1.12.0.3 Beta, 1.11.1, 1.11.2, 1.11.4
Retrieved
It looks like it has no fancy graphics at all. Cause it doesn't have lighting of it.