Excessive "Server description" changes being logged

Question

I have a replica set running 3.4, which is used by a Rails (4.2.7) application with Mongoid5 (5.1.6)

We're getting excessive "Server description has changed" posts to our logging system that don't indicate a change at all (see below.) The platform is running fine, aside from these logging messages. I've searched online, and can't find anything about what this might mean. Here is a sample of the posts, which occur every 10 seconds.

D, [2016-12-14T07:49:53.882124 #20003] DEBUG -- : MONGODB | Server description for mongo2:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:49:53.892663 #20003] DEBUG -- : MONGODB | Server description for mongo1:27017 changed from 'primary' to 'primary'.
D, [2016-12-14T07:50:03.875711 #20003] DEBUG -- : MONGODB | Server description for mongo3:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:03.884555 #20003] DEBUG -- : MONGODB | Server description for mongo2:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:03.894815 #20003] DEBUG -- : MONGODB | Server description for mongo1:27017 changed from 'primary' to 'primary'.
D, [2016-12-14T07:50:13.878723 #20003] DEBUG -- : MONGODB | Server description for mongo3:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:13.886576 #20003] DEBUG -- : MONGODB | Server description for mongo2:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:13.900932 #20003] DEBUG -- : MONGODB | Server description for mongo1:27017 changed from 'primary' to 'primary'.
D, [2016-12-14T07:50:23.881659 #20003] DEBUG -- : MONGODB | Server description for mongo3:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:23.888644 #20003] DEBUG -- : MONGODB | Server description for mongo2:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:23.903119 #20003] DEBUG -- : MONGODB | Server description for mongo1:27017 changed from 'primary' to 'primary'.
D, [2016-12-14T07:50:33.884056 #20003] DEBUG -- : MONGODB | Server description for mongo3:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:33.890432 #20003] DEBUG -- : MONGODB | Server description for mongo2:27017 changed from 'secondary' to 'secondary'.
D, [2016-12-14T07:50:33.905094 #20003] DEBUG -- : MONGODB | Server description for mongo1:27017 changed from 'primary' to 'primary'.

Does anyone have any thoughts on what this might be?

Thanks.