I imagine that you're probably missing the Sun Fragment in the 6th Biome, it's the only one that is easy to miss as it won't pop up on your map when you enter the room. From what I've read and experienced it's always placed prior to the big drop in the last biome. So if you're hunting and get to the drop off, you've gone to far. There is a large room with a chest that doesn't show up on your map until you get closer, as you get close to chest it looks like the edge of the room on your mini map, but there will be a blue orb to shoot off in the distance. Once you create the bridge, you'll get the last piece as well as a data cube and audio log.
To finish biome research you need to collect the audio logs, glyph cyphers, and xeno archives.
The xeno archives are the easiest since they always show up in every run, you just can't unlock all of the holograms until you have all of the suit upgrades. If you're in the second run you should be able to snag them all. The 6th biome can be tricky as it can be easy to miss. The Archive is at the bottom of a pit that if you don't jump down you won't see the room. The room has a long gap with a chest at the end, with 3 large blocks to jump across. Jump down in the pit and the Archive is at the bottom.
It took me a while, but I've finally figured out what cyphers are left. When you look at the translations, it doesn't really tell you much other than how many cyphers are needed to complete the translation, but not what biome they are in. If you look at your resources, AS-AR-017 shows your collected cyphers in each biome out of the total in the biome. Here you can quickly see how many are left in each biome which helps when farming. I think I'm still missing a small detial though, because my last translation is at 83 of 90, but when I sum up all of the remaining cyphers it shows I have 9 left, so it doesn't quite add up.