People really need to stop obsessing over "fair". Fairness has nothing to do with the real world, and doubly less in DWP land.
The real question is whether this is correct. And under current guidelines it is. UC claimants are required to be available for work, and that includes interviews. If a UC claimant cannot attend an interview, then by definition they aren't available for work. And as we have seen, the system has an outcome for that.
Restart coaches have very little say in how they dish out appointments. Their main concern is to evidence the claimants they are assigned have complied with the Restart conditions, or the provider (ultimately the DPW in the guise of SERCO) will want their money back.
Personally I think it's a cruel system which enriches government chums at the expense of vulnerable people. However I realise that's not a popular view these days.
The only practical advice to the OP is to conform to the system. Which is probably less than helpful, but really the only way. The are no grounds for appeal because the system has been designed in a fairytale world of perfect childcare which has been politically promised. And we should all know that political promises trump reality.
Folk can probably tell I am glad I no longer work in that field.