When a hub gets rebooted, it renegotiates all channels from scratch, and that's a good way of fixing a connection that'd drifted off a bit. That's why things usually look improved after a reboot. The protocols the hub uses are supposed to keep everything ticking over nicely as it runs, generally they work well but sometimes needs that extra "kick", and they can't improve a fault that (like most faults) has a physical cause, like a damaged joint, a crimped or abraded coax cable, a fault line amplifier or the like.
If the underlying problem of a noise fault isn't found and fixed, then the problem recurs, as you might expect. A further reboot might temporarily help if the problem crops up again, but that's not a viable solution for a poor quality connection - it needs to work as advertised. You can try calling this in by phone as a reliability problem, and see how you rate VM's telephone support, factor that into your view of how to proceed. Any tech support agent who says it is anything to do with your wifi, or "we'll send a special signal to your hub", or "it'll settle down over the next few days" would be deliberate fobbing off. This needs a technician visit, and with an intermittent fault there's a possibility that you won't see a first time fix, you'd then be outside the cooling off period.
I'm not encouraging you to cancel: When it works reliably and as advertised, then VM is a good service and even at non-discounted prices the phone and internet packages are good value. I've been with VM for 25 years, that may tell you something. However, when things go wrong, you might reasonably conclude that VM's telephone support is outsourced to the same company that operates the Iranian Revolutionary Guards customer care line, and that every Virgin Media process, every tool, every contact channel, they all take design inspiration from Franz Kafka, and staff leadership from Mr Bean. If you really need the speed and can't get anything acceptable as an alternative, then stick with it, and VM will eventually get this fixed, although in some cases customers need to be very persistent. Getting complex or intermittent faults solved very occasionally takes months.
