Encryptr's security bits are likely all implemented in the crypton framework. If you search the repo for that function (randomString), you'll see that it's only used in one place: to propose a new password (https://github.com/devgeeks/Encryptr/search?utf8=%E2%9C%93&q...). While it'd be best to not have any bias at all, this low bias only assists people trying to brute force passwords created by encryptr.

Crypton itself has been audited a couple times by crypto persons, see https://crypton.io/docs/security/audits.html

(disclaimer: i used to work at spideroak, but neither on crypton nor encryptr. i still think they're all awesome though)