Problem:
DbHistoryEventHandler#insertHistoricVariableUpdateEntity makes an explicit history level check for FULL before inserting a historic variable update.
When using a custom history level, variable updates always miss.

Should be:
Should rely on Context.getProcessEngineConfiguration().getHistoryLevel().isHistoryEventProduced() instead.

Possible solution:
Perhaps the check can be removed entirely at this point if the calling methods already make the check for the history level.