There could be several reasons for this.
On the exchange side, there is a flood of authentication requests which can sometimes result in a backlog, where some requests may be delayed or dropped to relieve latency on requests. Some Telkom exchanges are also not able to cope with Eskom outages (i.e. they don't have reserve or alternative power) so they go down during the outage and take some time to come back online (sometimes Telkom need to get involved).
Also, a similar things happen when there is an outage on our side. A flood of new requests hit our servers (and sometimes there is already a backlog) which sometimes causes a delay in accepting the new authentication.
Your router should automatically redial after every successful attempt, so you needn't worry about doing anything on your side. But if it takes more than 10-15 minutes after the outage is over, you should probably contact our support team to troubleshoot with you.