When you give yourself for example a diamond axe with a special attribute is attack speed of 1, you don't get it. Instead it gives you a diamond axe with no attack speed.
How to reproduce:
/give @p diamond_axe{Unbreakable:1,AttributeModifiers:[
{Slot:"mainhand", AttributeName:"generic.attack_speed", Amount:1, UUID:[I; -1, -1, -1, -1]}]}
To my knowledge, we can't use attribute modifiers on bedrock, I tried the command you listed, and it just gives an error. If this does actually work and you know how, please let me know.