Seems an odd problem this but, if anyone is interested I too had this exact problem with my original Humax Freesat box i.e. no U& Freesat channels but Sky arts working OK. Delete and re-tuning had no effect on the problem.
I resolved the problem by doing a factory re-set. Of course normally you would lose all recordings, timed recording settings and any other personal settings.
I was fortunate in that I have two original Humax machines, one of which is really a spare and has nothing of merit saved on it so, I put the spare hard drive into my main machine and did a factory re-set. Once complete I put it’s original hard drive back in and all the recordings, timer settings etc were unharmed. Of course personal settings, volume, OSD transparency etc needed re-setting.
The point is that a factory re-set will cure the problem but maybe at the expense of recordings etc.