Just for other user's consideration...
Our #Roku 3 (4230U) did not recognize a 32 GB SanDisk MicroSD HC Ultra Uhs-1 Memory Card. I plan to uninstall some of the (many) unused channels to see if that helps.
I remember that Roku reccomended a certian brand, but I cannot recall which one ATM.
I will try and see and post back later.
Maybe this is why ...or maybe this is the one and you already know this just trying to contribute here in positive ways.
Well I must have been remembering something else, pretty much, anyway, but here is the link to read ..just in case ya have not seen it.
Honestly when I put one in I did not really notice any difference in loading apps....my experience only.