8 days between shots should definitely be enough time to repin a site IME. Only time I could see it not is if it were a new site you weren’t pinning in the past. Is the carrier oil of this cycle the same as before? You really have a few options:
Assuming it is the same carrier oil you’ve had no issues with before, order sterile oil and dilute your shots by drawing half part gear half part oil. If the concentration of gear or BA/BB is the issue this will solve it. It’s less than $10 legal and domestic. A very easy thing to give a shot.
Introduce more sites to allow the others more time to absorb. The next most common option is delts and I would throw them into the rotation. If after 12 days your oil isn’t absorbing that would be alarming. Even 8 is a long time man.
Go to ED shots with less volume alongside introducing delts. So even though you’d be hitting each site every 6 days, it would be with half of the oil volume which would likely absorb better.