I know the crocodile effect from past – there was some problem with:
a) Vulcanizing – water in vessel and partly too less vulcanizing property of lining
b) Soft lining compound
To identify root cause it is necessary to check:
In case of a) – hardness lining and cover is too low – in case we make oven treatment 100 °C, 6 h the crocodile effect will be reduced a lot
In case of b) – hardness lining too low, cover o.k. – in case we make oven treatment 100 °C, 6 h the crocodile effect will be reduced only a little
I hope,. My reply helps a little.