And yet it didn't improve, right? I suggest taking the chance and bumping it up just a smidge to 6. We've got people who say 5.5-6.5 is fine in coco but you can look at those charts and see for yourself, just below 6.0... like somewhere around 5.95 or so, plants can't make use of calcium even if it's available to them.
Where I see folks have success is they'll start in the lower pH range in soulless mediums (haha, autocorrect did that and I'm leaving it!) like 5.6-5.8 and as the plant gets a little bigger they move it to 5.8-6.0 as the nutrient demand shifts.
But at the end of the day here's my take. Younger plants don't have much need for calcium yet and they are normally able to metabolize what little they need, except for one problem. And that is the electromagnetic wavelength generated by LED lighting strips it of its calcium and magnesium and it leads to a deficiency you wouldn't encounter normally until a later stage where you would have already adjusted to a slightly higher pH in preparation of the demand.
So like what do ya do... add more cal mag? Back off the lighting? Adjust your pH?
And just a final thought, not sure how you are getting your pH readings but if it's a digital pen they are prone to being off a little, so you could be even lower than you think... but strips or reacting agent drops, not so much.