devtrackers.gg
Which map failed to open? We have checks to ensure that Zana's Maps support her missions, but something may have fallen through the cracks. For example, not all maps support being Blighted, but she shouldn't offer that mission on such maps.
Though I can't tell from this screenshot if it was a Blighted Map mission or a regular Blight encounter mission (both have the same tracker text).
Also, did Zana really not offer you another map/mission? Normally, if the mission area fails to generate (as seen here) then she will restart the mission after around a few seconds and let you choose another. There was a bug last league where she could occasionally offer Blighted Maps in map types that don't support it (which we fixed), where those areas would fail to generate with that same error message, but at least she would always restart the mission in such a case. I have not seen this fallback mechanism fail before.