I found I get this problem when I have been on holiday to Spain.
I get to a technical section – have to stop for whatever reason & then struggle to get going again, as I can’t clip one foot in. I end up careering down stuff with one foot slipping around struggling to clip-in & not really concentrating on the trail obstacles that are coming up, as I am concentrating more on why my foot won’t clip in.
I bought some spds with the plastic cage round them to try out thinking it would help me in those ‘can’t clip in’ moments as I would have a big enough pedal base to carry on riding until I could clip in properly. But, in practice I found it made little difference.
I think I should spend more time practising getting clipped in while track standing so I can sort myself out before having to tackle the next section of trail.