Answer: I suspect that you have several varieties of grasses in your lawn. Having a variety of grasses in a lawn is good. Some grow best in cool weather and some grow best in warm weather. Since autumn is just around the corner, the cool season grasses are probably taking off and the warm season grasses are beginning to slow their growth. This is why you have various heights in your lawn even though you mow regularly. About the only way to avoid this is to have a mono-culture - a single grass variety. You can achieve this by digging out the faster growing spots and reseeding them with the same grass variety that is in the other parts of your lawn.
Best wishes with your turfgrass!
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