don't give up on your bridges so easily
Apr 23 20:29:37.000 [notice] no known bridge descriptors running yet; stalling Apr 23 20:29:37.000 [notice] Our directory information is no longer up-to-date enough to build circuits: No live bridge descriptors.
If you have one bridge configured, and it hiccups or otherwise you fail to get all the service you expect out of it, you'll mark it down. Then your Tor won't work for 15 minutes or something until you fetch its descriptor again and notice it's up.
Marking relays down when they fail to provide expected service is fine if there are thousands of relays to choose from. It makes things much flakier if there are only a few and you mark them all down.