It seems your LNB has partially failed hence can’t lock on some frequencies. Simply change it . Changing it does not need a technician unless dish is mounted on top of a steep roof .
First angalia kama kuna kitu inaemit interference hapo karibu. Labda kama kuna wifi ya mtu ameweka recently, ama kuna ISP/MSP ameupgrade booster zao ama kuweka karibu na kwako, ama umenunua allion na ukaweka radar detector na unapark karibu na dish. In short yaani any form of RF inteference.
Kama hakuna, nunua lnb ingine. Hiyo yako may have seen better days, na ureplace na cable pia. Yaweza kuwa imefray mahali na the cooler temperatures za usiku ikicontract contact point inapungua.
Pia angalia kusiwe na fala dush isiwe inaroost kwa dish yako.
Hairline fractures kwa lnb could mean of the signal directed to the lnb, not all of it makes it to the converter. Fray on the cable means not all of the signal is being transmitted. For the RF inteference I know you know when some signals operate at close frequencies they tend to intefere with each other. Oh, and electrical inteference. The crackling sound coming from sockets or an unstable voltage also inteferes with transmission and operation.
Had a similar problem back in 2009. The LNB could pick some TPs and draw blank on others. My problem was caused by fixing the f-connector while decoder was on hence the gradual attrition . I swapped LNB , maintained the same skew and fixed the problem .