By the time you need to think about adding more weight or the number of reps, you’ve figured out that your body has adapted to what those in fitness circles call your current “training stimulus”—in other words, you’ve made progress! Unfortunately, as you know, the journey to strength isn’t a nonstop flight to funky town.
Start out with low reps (but also low weights as well) for a month to focus on technique. I have found that sometimes with high reps, fatigue sets in and form breaks down… People tend to brute force the weight up instead. After the initial learning month, I agree that working on higher reps is safer for most people, but there comes a point that weight must be increased for more stimulus and adaptation.
At the end of the day it really is the long-term view that your coach or trainer is providing. Are they managing your total training volume vs. recovery appropriately? A good trainer will have a road map laid out for progress. This is a good question to ask about when vetting a trainer or coach!