Stepdown process started, can't checkout sessions except for killing

Yesterday we received a wave of bug reports our Node.js MongoDB driver with which we are connected to CloudAtlas.

2021-09-07T02:33:33.338615670Z 2021-09-07 1zz4:33:33:337NZ [ERROR][Application]: Error: ERROR:Exec error resulting in state FAILURE :: caused by :: operation was interrupted
2021-09-07T02:33:33.338645798Z STACK:MongoError: Exec error resulting in state FAILURE :: caused by :: operation was interrupted
2021-09-07T02:34:15.975509928Z 2021-09-07 14:34:15:974NZ [ERROR][Application]: Error: ERROR:Exec error resulting in state FAILURE :: caused by :: operation was interrupted
2021-09-07T02:34:15.975539600Z STACK:MongoError: Exec error resulting in state FAILURE :: caused by :: operation was interrupted
2021-09-07T02:35:32.557043399Z 2021-09-07 14:35:32:556NZ [ERROR][Application]: Error: ERROR:Exec error resulting in state FAILURE :: caused by :: operation was interrupted
2021-09-07T02:35:32.557073176Z STACK:MongoError: Exec error resulting in state FAILURE :: caused by :: operation was interrupted


2021-09-07T00:03:15.557242233Z 2021-09-07 12:03:15:556NZ [ERROR][Application]: Error: ERROR:a stepdown process started, can't checkout sessions except for killing
2021-09-07T00:03:15.557306312Z STACK:MongoError: a stepdown process started, can't checkout sessions except for killing
2021-09-07T00:03:15.561886825Z 2021-09-07 12:03:15:561NZ [ERROR][Application]: Error: ERROR:a stepdown process started, can't checkout sessions except for killing
2021-09-07T00:03:15.561903059Z STACK:MongoError: a stepdown process started, can't checkout sessions except for killing
2021-09-07T02:35:54.927173707Z 2021-09-07 14:35:54:916NZ [ERROR][Application]: Error: ERROR:a stepdown process started, can't checkout sessions except for killing
2021-09-07T02:35:54.927206107Z STACK:MongoError: a stepdown process started, can't checkout sessions except for killing

We’ve never come across such errors. Anyone have ideas what they mean?