Haven't noted this issue being discussed here but there was a new Experimental update released today which is supposed to address this problem. Build number is 62637 and hopefully it will be released to main in the near future.

Patch notes copied and pasted from HG's post on Steam and tossed in the two from 25 and 27 July:

Experimental Branch 29/07
•Fixed an issue that caused the hit indicator to flash incorrectly for some ship and Multi-Tool modes.
•Reduced the priority of the Emergency Broadcast Detector and Salvage Opportunity hints so that they do not block other mission messages.
•Fixed a number of issues that could cause the Anomaly Detector and Emergency Broadcast Detector to perpetually fail to locate an object, blocking progress.
•Fixed an issue that could cause inappropriate items to appear in the artifact crates at the heart of buried ruins.
•Expanded the Nexus exploration mission to also include flora and minerals.
•Fixed an issue that could prevent other people's discoveries from advancing multiplayer exploration missions.
•Fixed a number of issues that could cause planetary creatures to fail to spawn.


Experimental Branch 27/07
•Added procedural atmospheric fog effects to the interior of derelict freighters.
•Fixed an issue that caused a soft light to follow the player into caves and other dark spaces.
•Fixed a number of small visual artifacts in the lighting system.
•Fixed a crash that could occur during loading.
•Fixed a number of issues that could occur when declining or accepting a group invite.
•Fixed an issue that prevented the Chef title from unlocking after impressing Cronus.
•Fixed an issue that caused a number of lighting issues for metallic surfaces.
•A range of new base building parts have been added. These are based upon the decoration inside derelict freighters. The blueprints can be acquired by searching salvage crates found inside derelict freighters.
•Fixed an issue that could cause the game to become unresponsive during loading.


Experimental Branch 25/07
•Fixed a number of visual issues with the intensity of starship trails and engine glow.
•Fixed a crash that could occur during procedural generation of a derelict freighter.
•Fixed a crash that could occur when calculating creature navigation paths.
•Fixed an issue that could cause particle effects to stop playing.
•Fixed an issue that could cause a unpassable corridor to be generated in certain derelict freighters.
•Introduced a number of small optimisations.
•Fixed an issue that could cause very large save games to crash during load.

I can confirm that since 2.60 the spawn rate of fauna is much reduced now. Fauna does spawn but much less frequently, even on planets with abundant fauna.

I really hope this gets fixed soon.

It had been over a week since being able to complete 100% on any planet and in many cases as soon as 50% were discovered then nothing spawned included previously discovered. On some other planets no fauna spawned.

However, with yesterday's Experimental I was able to discover all on one planet and finish off another so the fixes seem to have worked or at least helped.

Ok so I just downloaded and installed the experimental patch 62637, and something seems to have changed, I'm now seeing fish whereas I wasn't seeing any before. However there still seems to be a lack of terrestrial creatures, I didn't see any at all during my quick test. I also saw a few flying creatures but only in one spot so it's hard to tell if they are spawning correctly or not.

I've been playing with the 62637 update some more and it does seem that creatures are spawning more often, but there's still something not quite right here. Sometimes they seem very slow to spawn, I found that in some case I'd have to sit in the same spot for a few minutes before anything started to spawn and that if I kept moving around nothing would spawn.