Understanding Society User Support

I was wondering if you were able to help me out at all with some clarification regarding the amount of missing variable associated with the “receive rent rebate or rent allowance” variable (_renthb & renthb_bh) for both BHPS and UKHLS for the years 2001 – 2019. Also, I am only including those who complete a full individual interview (ivfio = 1) and full household interview (ivfho = 10).

I am trying to create an indicator that just simply represents if an individual respondent receives housing benefits or not, but I am getting large amounts of missing observations primarily for those who are classified as “Local Authority Renter” or “Housing Association Renter”.
Even after I set all homeowners to 0, those living rent free to 0, and those paying 0 rent being set to 0. Out of all the Local Authority renters, about 18% still have a missing value and 11% of all housing association renters have a missing value still (mostly tends to be the Inapplicable -8 value).

I was mainly wondering is this normal? Is there any particular reason that so many social housing renters recorded an inapplicable value to begin with? For instance, looking at the UKHLS version “_renthb”, I get 10,374 (31%) out of 33,034 local authority renters with a value of -8 (inapplicable).
Apologies if this has been spelled out somewhere in the questionnaire or the user guide but I cannot seem to find an answer.

Kind Regards
Jack