Boost lost in low rpm for hundreds of kms driving then returns

I have a turbo charged 4.6 2v ford explorer running Holley terminator x. Out of the blue it lost boost and wouldn’t make any until high in the revs 4500+ where before begins to make boost around 2500. I originally thought the turbo had failed so inspected it and found all looked well (weird) at that time I thought all boost was nonexistent until I climbed it higher into the revs and it finally came in slowly but actually boost spiked the first time I pushed it. It stayed like that for well over a week with daily driving and hitting boost occasionally on the freeway with a bit of effort. Today I hit boost on the freeway way 2nd and short shift to 3rd I heard it break up during the short pull. The weird thing is next time a came to a stop and left boom everything is now back to normal making boost as it did from day one. I can’t work out how it’s possible?

Stuck wastegate valve/ actuator by your description assuming it wasn't caused by significant consistent misfires.

Now it’s back at normal rpm but breaking up and going really lean under boost, light throttle, cruising, idle ect is fine just under boost bad break up and fluctuating lean around 13-14 afr when target should be 12.5-11.5ish

That sounds like misfires. I'd be checking plugs/coil and individual injectors. If it's only happening on load it's far more likely to be ignition side than fuel. Misfires will read lean regardless if the correct fuel is being delivered or not.