No maps from Expedition encounters with % chance to get extra map?

So I know its only a chance, but every time (total of 4 encounters so far) I find Expedition with %chance of droping extra map from runic or chest I dont get even single map. In all cases I was able to pick up the node with first or seconds explosion and focused on getting as much relevant targets (chests or skulls depending on bonus type) as I could with that and subsequent explosions.

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The screen below shows last encounter - 12 skulls cracked, not a single map dropped. Ive checked with my loot filter ofc to make sure its showing maps and checked with toggling z and holding alt to make sure im looking at all (screen does not show that - f12 dont work when holding alt).

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Is it just me being very unlucky or is tere a problem with that modifier?

Outcome of the last such encounter