This is the error:

Error: assert.soon failed, msg:no balance happened

sharding_rs1.js does a bulk insert and then waits for the balancer to spread all the chunks out evenly. It currently waits 2 minutes. Now that the config primary continuously steps down, the balancer is frequently delayed trying to contact the config primary and balancing takes longer.

Solution would be to increase the wait time, to say 3 minutes.