I am having the same issue on the mobile platform. Trying to use a 5s Rocktooth and 5s Valerie to upgrade.

I have problem with skullsworn on 5* to use him to upgrade kael to 6*. I have wornings that skullsworn can fuse another champion but when i click to sacrifice him to upgrade rank for kael  nothing hapend.

Same problem. None of my 9 or 10 fusable players can be sacrificed to upgrade my Champions. I can't six star Kael, my first because of it   Therefore I can't clear Spirit Keep level 10 or Fire Knight 8.  

This sucks!!!

Happened on mobile version!

Same problem...i can not use a champion to upgrade rank of another , if this champion can be used to fuse others. even thought i choose to sacrifice him.

I have the same problem. I want kael to rank up to lv 5 and have 2 Sorceress. i can use 1 and not the other. the diffrence between them is that one has some treshitems and the other not. so my guess is that the allerts of "it is a champ that can be fused" and "their are items that will be lost" get bugged. but i dont want to pay the silver to remove the items.

I have been having this problem ever since the last major update.

If there is a second champion in my inventory, I cannot, even though I tell it to sacrifice, get the game to do it.  I am now trying to go for the event just announced, and have 6-10 of different champions to ascend, but I have at least 10 different champions that will not actually work as fodder for ascension.

I am coming to loathe any PC who has the little whirl icon on it.  Please just take this feature off, and let me choose for myself.  The Upgrade for this Is full of bugs and errors.

I am using a new Dell gaming PC on Windows 10 as my platform, and just downloaded the latest version.  I have good internet.

what's completely frustrating about this bug is that you can be farming your fodder champion along, and then get to where it's time to feed it to the better champion you want, and there is no predicting whether the game will actually do what it says it will do.  generally, I am finding that if the champion has the "whirl" symbol on it... it's a 3 in 10 proposition whether it will be accepted to being ignored.

The most egregious champions for being rejected are:

Heiress

Twinclaw

Runic Warder

Myrmidon

Gnarlhorn

jonny725 said:

I have the same problem. I want kael to rank up to lv 5 and have 2 Sorceress. i can use 1 and not the other. the diffrence between them is that one has some treshitems and the other not. so my guess is that the allerts of "it is a champ that can be fused" and "their are items that will be lost" get bugged. but i dont want to pay the silver to remove the items.

edit: i found the option to destroy the items. after destroying them it worked. just check if you still have items on the champ

Thanks bro it worked <3

II'm also having this issue. I can't use my 5* Skullsworn to upgrade my Skullcrusher to level 6*. 

This is on mobile.