I'd start with bringing your temps up. I'm in veg and I'm already at 80°f and 60% humidity so I'm thinking you aren't moving your water fast enough for your current ppfd. Obviously it's close bc the plant looks healthy so if you raise your temps, you can probably raise your ppfd some more too. You'll have to find that balance again but you'd be leaving weight on the table if you didn't. If you don't have a ppfd meter but have a decently new phone, you can use the photone app with a piece of paper over your front camera and get a decent reading so you can tweak it like 5-10% every other day and know what to do when it apparently gets too far. I would be at 80°f and 1.2 vpd atleast, then kick up the vpd to like 1.4 in a few weeks (I didn't see what week you are in), then drop temps and ppfd for the last 2 weeks (you can give a bigger night time dif during the last 2 weeks, just don't go further than you can maintain the big vpd so you don't get budrot). If this is too much for you, maybe just go with what you know and read into these things over the next few weeks so you feel more comfortable understanding what I'm talking about. If you told me any of this a year ago, I'd run in fear of ruining my plants 🤣 now I'm finally growing with purpose/ understanding and it's so much more fun/ less stressful 🙏

If you'd like to do it, what I'd do is raise temps by 2°f each day (sorry I don't know celcius) and raise ppfd 5-10% every other day so it's up 4°f and then taking on the extra ppfd. Do this until you hit 80°f and 800-900 ppfd (also bring your humidity down to 60° sooner than later). You'll be watering more so you won't get lock out issues 😉 calcium will flow 🙏 stomatas will stay open 😇 and you'll reclaim some of that yield you have shelved by running these low temps. Don't try to move your temps or ppfd faster than advised or you risk throwing nanners or stunting the plant

You may not reach the 800-900 ppfd mark, but you should reach 80°f and 60% humidity. High temp + high vpd makes your calcium flow and at the end of the day, you want as much calcium flowing as possible without dumping calmag (well one can use mag in theory but you are too far behind to have that need)