This is bugged for me - been on a Planet for hours driving around, been back into orbit and down again 3 times now. Original scan said 5 biologicals. I picked one from the filter ( not the bacterial! ) fly down to the 'teal' area, but all I can find is Tussocks(also not what I selected in the filter), which I've scanned and collected, but I can't find anything else! ('PRU EUQ JD-J D9-3 4A) if anyone else is in the area.
What I do (your mileage may vary):
Fly to locate the organism, then drive around to collect scans. Bacteria especially are much easier to spot from the air, and airborne, you can cover more ground.
Fly inverted at low speed and low elevation, looking "up" at the ground unobstructed. Leave the planet and come back if an area isn't working
When you can't find it on flat ground, look on high ground, and vice versa.
When you can't find it with the naked eye, try night vision, and vice versa.
When you can't find it on the daylight side, check the night side, and vice versa.
When I can't find a fungoid, it's almost always on hilltops in rough terrain in the dark.
Osseus Spiralis are horrible for spawning everywhere (according to the heat map) on planets that have very few rocky areas for them to actually spawn in and so can be very difficult to locate for very little payout.
Bacteria, obviously, are just difficult if they are the same color as the terrain. Night vision sometimes helps with this.