Looks like it's .11 to .16 mm (.0044 to .0063 in) for both. Screenshot attached.
Also, here is a link to the workshop (service) manual:
https://www.kubota.cz/data/soubor/WSM_RTV400_EN.pdf
I'm having the same issue here. So far I've done engine oil change, transmission/differential oil change, new spark plug, new fuel injector, both air filters, added inline fuel filter, and a new 300CCA battery. The issue persists.
Would be great to hear if the valve clearance adjustment fixes this. Please send updates!