The Homebrew Launcher Channel has no official support on Tiramisu, the Mii Maker HBL is the official way to launch homebrew.
My first suggestion would be to just transition to using Mii Maker HBL. If it helps, you might want to consider downloading the latest Homebrew Launcher build from
here. You'll need a GitHub account to access that page, so I've also attached the download to this post, if you trust random message board attachments.
That latest build can replace your current one in
sd:/wiiu/apps (use the regular build, not the debug one) and allows you to return to the Wii U Menu by pressing Home, instead of having to exit via Mii Maker--if you do need Mii Maker, you can simply press the Minus button, as noted in the bottom left. For me, the inconvenience of exiting via Mii Maker was the only thing keeping me on the Homebrew Launcher Channel.
If none of that interests you, you can keep using the Homebrew Launcher Channel with a couple of workarounds. If you have some older ELF format homebrew, e.g. ftpiiu, you can launch that, exit it, then launch the RPX homebrew you actually want to load and it will run fine.
Alternatively, you can remove the
hbl_installer.rpx from your
sd:/wiiu/environments/tiramisu/modules/setup directory (path is from memory, if I don't have it exactly right, have a look around). This will mean the Homebrew Launcher is no longer being injected into Mii Maker, and the legacy Homebrew Launcher Channel should function normally.