I was also affected again from approximately 10:30PM - same as before, the modem is synced but can't establish a PPP session.
It was still down this morning for me, outside of the maintenance window, so I gave them a call. Interestingly, I had two PPP sessions established (due to my backup firewall also trying to connect, oops), which understandably caused some problems! After I resolved that though, all good. Not quite sure why that happened, this is the first time though there's actually been a PPP failure since I clustered the firewalls so not really had a chance to experience this failure condition before!
Whilst I was on the line to them, I asked if they had any more details about the weekend outages. Apparently Vodafone had been doing some work on the backhauls Zen use, which affected a large number of exchanges. I also asked if there was a way to get automated notifications about planned maintenance as listed on the status page, unfortunately there isn't but they mentioned they could log it as a feature request if I dropped them an email. Even if most of the time having my area code listed means there's no impacted (e.g. because the maintenance results in reduced redundancy rather than a full outage), it'd still be useful personally to get a heads up about any potential issues so if something does arise, I know why rather than having to troubleshoot from scratch!