@Animage55 Do you remember the version you updated from?
Other than that try to update Tiramisu (redownload from https://tiramisu.foryour.cafe and extract the files to the SD card, overwriting existing ones). Normally it should show an error in case Tiramisu is out of date but there seems to be some issue with this currently.
In case this also doesn't help do not use HBL Channel but the one injected into Mii Maker (reboot your Wii U and go straight to Mii Maker without opening any other app before, then try to start NUSspli from this HBL). Reason for this is that HBL Channel does an IOSU exploit but this overwrites parts of Tiramisu, creating the weirdest issues. Rule of thumb is to not use any apps which do own IOSU exploits (this is true for any CFW, Tiramisu just seem to be more sensitive to this than previous CFWs).
Other than that try to update Tiramisu (redownload from https://tiramisu.foryour.cafe and extract the files to the SD card, overwriting existing ones). Normally it should show an error in case Tiramisu is out of date but there seems to be some issue with this currently.
In case this also doesn't help do not use HBL Channel but the one injected into Mii Maker (reboot your Wii U and go straight to Mii Maker without opening any other app before, then try to start NUSspli from this HBL). Reason for this is that HBL Channel does an IOSU exploit but this overwrites parts of Tiramisu, creating the weirdest issues. Rule of thumb is to not use any apps which do own IOSU exploits (this is true for any CFW, Tiramisu just seem to be more sensitive to this than previous CFWs).