We're using dynamic docker slaves which are spun up to build and then immediately deleted when the job is completed. We ran into an issue where the git polling was not working and tracked it down to the use of a parameter in the Branch Specifier field (See screenshot). 

Having to hard-code this value into the field is fine but we prefer to use a parameter to avoid having to hard-code this value in other related fields which adds the risk of missing one when making a job change.

The same problem seems to also affect the Lightweight Checkout option.