What could this be

tip burn from being a little overfed. looks like a bit too much N too (dark/glossy). would need more info. a soilless or hydro context would be a matter of looking at the ppms of each molecule you feed and making some specific adjustmetns to that ratio or overall concentration. with soil, it's more difficult with more unknowns. Reduce concentration or frequency of your fertigation. See how it plays out over next couple weeks. if this has beena slow progression, make a small adjustment. Also, be more patient when choosing to add things (future consideration) as it is much easier to add than take away. always be certain befor you add to fertilizer in case it is not the actual 'fix' to a problem.. now, it's 2x worse, lol. While it's not a big deal right now, it's important to get that equlibrium back into the goldielocks zone... if it built up, it will continue to build up and get worse if you keep doing the same things. Take any necessary notes to avoid the situation next grow cycle. Once oyu have a few grows under your belt the plant should look nearly pristine seed to harvest -- some senescence expected at the very end no matter what, though some plants won't even show imminent death, if happy.

the leaf in the top right corner almost looks like pm.

I clearly wasn't paying attention. Its slightly over fed which is typical with that type of soil. . Its nothing to worry about.

That's very minor. The leaves are pretty dark but that could be the strain. Feed every other watering with soil and never give coco plain water unless its the final flush.

You can see by the very dark green leaves, very dark green, that whatever soil you are using, even if labelled "light", is too hot or has excessive fertilizers for this particular plant. Soil drying out has absolutely no effect on plants and being over fed. Start a diary if you want the best advice people can give you.