You have to many dynamic instances? Resolves all key issues and connects to instance the moment is up.

shh.sh

#!/usr/bin/env bash

declare -x USER=""
declare -x HOST=""
declare -x KEY1=""
declare -x KEY2=""

retry_scan() {
  while true; do
    KEY1=$(ssh-keyscan -t ecdsa "${1}")
    if [[ "${KEY1}" != "" ]]; then
      break
    else
      sleep .$(( RANDOM % 10 ))s
    fi
  done
}

retry_ssh() {
  while true; do
    if ssh "${1}"; then
      break
    else
      sleep .$(( RANDOM % 10 ))s
    fi
  done
}

get_host() {
  if [[ "${1}" == *@* ]]; then
    USER="$(echo "${1}" | cut -f1 -d'@')@"
    HOST="$(echo "${1}" | cut -f2 -d'@')"
  else
    HOST="${1}"
  fi
}

if [[ "${BASH_SOURCE[0]}" = "$0" ]]; then

  get_host "${@}"

  KEY1=$(ssh-keyscan -t ecdsa "${HOST}")

  if [[ "${KEY1}" == "" ]]; then
    retry_scan "${HOST}"
  fi

  KEY2=$(ssh-keygen -q -F "${HOST}")

  if [[ "${KEY2}" == "" ]]; then
    echo "${KEY1}" >> ~/.ssh/known_hosts
  elif [[ $(echo "${KEY1}" | cut -d' ' -f3) != $(echo "${KEY2}" | cut -d' ' -f3) ]]; then
    ssh-keygen -R "${HOST}"
    echo "${KEY1}" >> ~/.ssh/known_hosts
  fi

  retry_ssh "${USER}${HOST}"
fi