Hi! I wonder whether it is a problem of hub title, rather than engaging content. When a title does not reveal enough of what the hub is about, viewers may click to see more of what it is about and find it wasn't what they were looking for and immediately leave.
Also, in looking at some of your titles, (from my humble perspective) my impression is that they may be too long and wordy. A professional writer once told me to keep my titles to 6 words or less. Sometimes I go over, but I try to keep them short and to the point.
For example, your hub titled "How to make your computer run faster - just follow this easy guide!" could be shortened to "Easy Guide to a Faster Computer" or "Speed Up Your Computer - An Easy Guide" or "Slow Computer Made Faster - An Easy Guide". This last one would catch those Googling both slow computer and faster computer.
Or, your hub titled "What is ECU remapping & should I remap my car / van engine?" could be shortened to ECU Remapping for Car and Van, or ECU Remapping for Better Engine Performance. If engine or car is a stronger keyword than ECU, those words could be fronted, like "Car and Van ECU Remapping" or "Better Enging Performance with ECU Remapping". Hope this helps some!