Hi Joanna - points on a map are limited to 3333 in 2.1. That is up from 1000 in 2.0. This may be a reason ?
There is more to come in the future on this limit too. You may need to add a calculation condition on the map to limit the selection before rendering the map.
not the same but related, a similar limit on scatter plots (not maps) was raised far greater thanks to 'smart data compression' released in 2.0