you need to understand what you feed your plants to deduce any symptoms. e.g. if you provide lots of calcium, it's not calcium deficiency.. it is lockout. So, do consider recent behaviour. calculate PPMs of what you feed.
bloom nutes often have high levels of P and K. If either of these are 'boosted' too high, you will have calcium and magnesium issues... this is predominantly why people think they need cal-mag all the time.. more times than not it is their 'boost' formula or 'bloom' formula... there's no magic bullet. too much is simply too much.
good news is that looks mild and isolated. You can take your time with this problem and ensure you choose the right path.
also, you are fairly late into the life cycle. Some blemishes are inevitable.. or at least very difficult to avoid 100%. This won't impact quality or yield in any noticeable way, even if it worsens a bit.