Thanks Simon, I'll post up some info with the permission of Mike at midsummerenergy.co.uk who has been very helpful and communicative indeed in helping to sort this - the unit is with him now for testing tomorrow. This may hopefully help others who ever experience issues:
Considering it is a temperamental issue I thought it may have been software related. V1.30 was released in February and is the latest firmware version available.
I've spoken to Johannes [Victron]; there is no way to download the older firmware versions, or a way to flash it. He says it is very unlikely to be a software issue. I'll need to do an RMA when I receive the product and see what Victron say.
I have come across one or two units that have displayed this same 'reluctance' to re-start in the mornings or once the battery voltage has dropped below Float threshold. But not enough concrete evidence to suggest a known fault in the product range. If you know people who have reported this issue then it might be worth getting the serial numbers of the units and letting Victron know there's a problem. I'm surprised it occurred with the latest firmware version, though there are some known glitches with older versions.
Again, I need to take a look at it before I can confirm anything but I think it'll just be a case of replacing the unit with a new one. No reason to expect the new one to have the same, or a different, issue as they're generally very reliable.
I think it's worth letting forum readers know that there have been some known firmware issues with the Victron charge controllers, if that is indeed the case here. Regular firmware updates to their charge controllers do normally address these issues (though this requires the Smartsolar or the Bluetooth Smart Dongle). I get the impression Victron are slowly moving away from the BlueSolar range in favour of the SmartSolar, which makes sense in the long run. I don't have any problem with you mentioning this in your forum posts or mentioning our company as your supplier; if there are more people who have experienced this issue then it would be good to collate the evidence and provide it to Victron, as this is the only proper way they're made aware of intermittent faults and glitches. Let me know what you find out and I'll check your controller tomorrow morning.