I believe mushroom compost is quite alkaline because of the lime (please correct if I’m wrong) and alkaline soils can encourage scab on potatoes. Having said that I inherited a few bags of mushroom compost last year which I put across a few of my beds which didn’t look fully rotted down but over the year this has settled and given a nice texture. A few mushrooms poked up here and there. Some of my potatoes did have a little scab on them but nothing major. If anything it’ll be good for feeding the soil overall and improving it