Connection failed: Failed to decode base64

From time 2 time i see this error.
Call stack:
Error: MongoError: "Connection failed: Failed to decode base64."
at MongoClient.connect (https://deno.land/x/mongo@v0.31.1/src/client.ts:46:13)

my code looks like this:

export { MongoClient } from "https://deno.land/x/mongo@v0.31.1/mod.ts"
const client = new MongoClient()
const options = {
servers: [{host: MONGO_HOST, port: MONGO_PORT}],
credential: {username: MONGO_USER, password: MONGO_PWD, db: 'admin', mechanism: 'SCRAM-SHA-1'},
db: 'mydb'
}
await client.connect(options) // this line causes error