Sometimes even the best-maintained pools encounter a period of unexplained stress, or develop a "haze" that tells you as the owner ..."Something's not right". You show your CYA as 65-70, so normally we round-up which would require an ideal target FC of 5. You tested it at 4 earlier which is still within the acceptable range, but if any some point(s) it dropped lower (closer to 3), that could've been the problem. If the CYA was actually closer to 65 or 60, then we know that's a bit low which would cause stress on the remaining FC in the water.
But again, even when testing is 100% accurate, there are rare occasions where water might take-on some stress from environmental factors and it shows (lack of clarity, green/dusty clouds after brushing, dropping FC, etc). At least you had the awareness to know something wasn't right, and you have the tools (testing & bleach) to get back on-track as soon as possible. If you still have concerns about pollen versus algae, you could still increase FC a little to conduct an overnight (OCLT) before continuing. Maybe bump the FC up to about 7-8 just to get a good overnight comparison.
Along with the plumes of green, it's the haziness that concerns me. Either way, let us know how it develops and what you find out.