This category is used for agents, mixtures and exposure circumstances for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence of carcinogenicity in humans but there is sufficient evidence of carcinogenicity in experimental animals.

[...]

This list is focusing on the hazard linked to the agents. This means that the carcinogenic agents are capable of causing cancer, but this does not take their risk into account, which is the probability of causing a cancer given the level of exposure to this carcinogenic agent.

https://monographs.iarc.who.int/wp-content/uploads/2018/06/CurrentPreamble.pdf

The results in this case were deemed limited by the IARC, meaning:

[...] chance, bias or confounding could not be ruled out with reasonable confidence.

https://www.iarc.who.int/wp-content/uploads/2018/07/pr208_E.pdf

Seems to me like one should expect more concrete evidence after decades of active research on the topic.