Well
duh!
It's a known fact that lithium batteries will never be fully and properly balanced when you don't charge to 100 percent full on a regular basis. This is because every single cell has its own specific voltage characteristics, and there are enough variances between all of them, that when you don't charge to 100 percent, the cells working in conjunction with each other and how the BMS functions with them, will drastically impact overall useable output. Likewise, while you can improve battery life by not fully draining the battery everytime before charging, it is best to let it drain fully on occasion. The battery killer though is not charging to 100 percent, as the cells can get permanently out of whack with each other, and cutting the battery life significantly. And please don't compare what you do with your single battery cell phone in terms of charging to the multi cell ebike battery pack. Two entirely different animals here.
So your ' habit' of charging to 80 percent is a very bad one. Wherever you heard that from, you were highly mis-informed. You've already shortened the entire life of the battery, not just your range. So just stop doing it, unless you want to brick your battery prematurely.
Thanks though for proving the results to the EBR audience the very poor practice of short charging your ebike battery pack. If you want a full technical explanation why all this happens, rather than a lay person read, pm me, and I'll direct you to some credible links on the topic, not the bs on this topic that's all too frequently posted here at EBR.