If you're trying to do UT1 (70%-80% of max HR) training and instead you're doing UT2 (55%-70%) or AT (80%-85%), then you're not going to get the benefits you were going for.

Further, the only way you can accurately measure your rate of improvement is by comparing average watts across time at a fixed HR. So if your HR isn't at your target level then not only are you not going to be making progress at an acceptable rate, but you're not even going to know that you're not on track until it's already too late.