[Complete two purge missions at your level or higher withing 30 minutes] becomes impossible around level 60 , because none of the sectors spawn enough missions of that type, or at that level...

The problems started around level 60.
The 'second toughest' sub-sector (rating 60-65) spawn missions that are actually 60-, so these do not qualify.
The 'toughest' subsector spawns missions (66-68)+ which are too tough.
When there are missions created at 60-65, they are too few, or not the right type.

Story missions are not (reliably) of the correct type.

I can not use tarrot cards to get get low-level missions to 60, or the description of the tarrot cards that affect level change once you achieved the level (not sure which).

I tried clearing out all missions in a subsector to trigger a re-spawn... again ot enough missions, but now I am at level 63.

At lower levels completeing these challenges was fair enough because enough of the right level/type were available.

Or am I missing something?