I am playing on PC Win 7, and at about 195 days in-game. In addition to the ladybug respawn issue, I have steadily noticed entire areas of the map becoming essentially "dead zones" with no respawn of previously commonly encountered enemies. This was definitely evident after the August Update, but I had minor suspicions even earlier, as far back as the second post-launch hotfix patch. I have several examples of this issue, as follows:
Orb Weavers
Orb Weavers were a common sight both in the Hedge area and all along the wooden log walls on either side of the Oak Tree; however, for at least 60+ days, no orb weavers have respawned anywhere in the Hedge, either in the canopy or the ground. I still see spiderlings, but the Broodmother and any Orb Weaver spawns are completely gone. Furthermore, none are respawning on the western log wall, including around the tipped over potted flower near the pond. The Oak Tree itself still respawns orb weavers (though it seems they are fewer - likely due to the lack of western respawn/roaming), and respawn continues along the eastern log wall as expected. NOTE: I do hear a trapped spider in the trunk of the tree supporting the Hedge Lab, but no other orb weavers exist there. I have no indication of a stuck or trapped spider anywhere near the Oak tree or western log wall that could potentially be causing the lack of spawn in that area.
Stink Bugs
Originally, Stink bugs had about five guaranteed spawn locations: 1) 2-3 in the dry grass north of the pond, 2) one usually fighting with an orb weaver near the wooden log wall just west of the Oak Tree, 3) 2-3 near a dirt mount and field station in the eastern dry grass (somewhat near the field station in the larva cave), 4) 2-3 in the barren area a little NW of the Ant Hill by some dandelions, and 5) 1-3 under the handle of the rake laying on the rock near the Haze. As of this writing, I am only able to find one stink bug at location (1), and have not seen any respawn for at least 60+ days at locations (4) or (5).
Bombardier Beetles
As in the case of stink bugs, Bombardier Beetles have five spawn locations: 1) two in the far east end of the wooden log wall, 2) one by the far west end of the log wall around the large flat rock, 3) 2-3 near the western side of the Hedge almost under the red deck/porch, 4) one near the entrance of the field station in the larva tunnel, 5) one usually on top of the large rock that the rake rests on near the Haze. As of this writing, no bombardier beetle respawn has occurred for 60+ in-game days at locations (4) and (5).
A Comment on Ladybugs
Ladybugs will respawn for me on the release of a patch usually, but the August Update patch still placed a ladybug under the world (or possibly failed to remove it as it said it would) such that I had to kill it using the now consumable gas arrows. I am currently waiting to see if doing so fixes the lack of respawn for them, but after 4 in-game days, I have not seen any. The location itself was interesting: from the surface, the ladybug appeared to be underground in a randomly raised area of dirt near the southern-most laser with the "mite cave" as part of the story mission; however, once I went into the cave, I realized that the ladybug seemed to be spawned directly above the rocky "light shaft" location near the end of the cave. It must have been spawned stuck between the ceiling of the tunnel entity and the floor of the main map. I checked this by noting my location on the map both inside and out of the cave system where I heard and killed the ladybug with the gas.
From what I've gathered, it seems that ladybugs (and possibly other creatures) are spawned in "batches". Spawn three in, once all three are killed, spawn another three. If this is the case, I would strongly recommend reworking the respawn system. Having to hunt down the last creature to ensure a respawn, especially if they are still able to spawn stuck in entities, is a real pain. It may be better to set a maximum spawn count for them, and a regular spawn check interval. On check, it looks at the number in existence, and if it's less than the max, spawn more in to that number. With that check, it should look at the existing entities and see if their current position has changed significantly from their spawned in location. If not, it likely indicates a stuck entity. Force kill it and spawn another in its place elsewhere.