It could be either LNB or cabling not dish alignment. If it was it would have been constantly the case and not intermittent. If I remember correctly, you said you were receiving over 900 chanels on ascan so, that also rules out dish alignement.

If you have confirmed that it works fine at another place, simplest way to get your problem fixed is to replace LNB and cabling. A bit drastic, but will solve your issue hopefully.

If you dont want to reaplace whole lot in one go, you could try different ports on LNB, they are essentailly different LNBs. If still the same, then replace the cable.