Any warning message or crash log?

If it's not top on the load order it just starts up with the usual message where it tells you to disable mods. I did take a look at the additional info and this is what came back:
Exception while loading mod Stairs at C:/Users/zpyde/Documents/Klei/OxygenNotIncluded/mods/Steam/2012810337.
HarmonyLib.HarmonyException: Ambiguous match for HarmonyMethod[(class=TransitionDriver, methodname=BeginTransition, type=Normal, args=undefined)] ---> System.Reflection.AmbiguousMatchException: Ambiguous match found.
at System.RuntimeType.GetMethodImpl (System.String name, System.Reflection.BindingFlags bindingAttr, System.Reflection.Binder binder, System.Reflection.CallingConventions callConv, System.Type[] types, System.Reflection.ParameterModifier[] modifiers) [0x00059] in <695d1cc93cca45069c528c15c9fdd749>:0
at System.Type.GetMethod (System.String name, System.Reflection.BindingFlags bindingAttr) [0x0000e] in <695d1cc93cca45069c528c15c9fdd749>:0
at HarmonyLib.AccessTools.DeclaredMethod (System.Type type, System.String name, System.Type[] parameters, System.Type[] generics) [0x00036] in <2f5aaaa000594d07b9998f4cff1e9662>:0
at HarmonyLib.PatchTools.GetOriginalMethod (HarmonyLib.HarmonyMethod attr) [0x00049] in <2f5aaaa000594d07b9998f4cff1e9662>:0
--- End of inner exception stack trace ---
at HarmonyLib.PatchClassProcessor.ReportException (System.Exception exception, System.Reflection.MethodBase original) [0x0010f] in <2f5aaaa000594d07b9998f4cff1e9662>:0
at HarmonyLib.PatchClassProcessor.Patch () [0x00082] in <2f5aaaa000594d07b9998f4cff1e9662>:0
at HarmonyLib.Harmony.<PatchAll>b__10_0 (System.Type type) [0x00007] in <2f5aaaa000594d07b9998f4cff1e9662>:0
at HarmonyLib.CollectionExtensions.Do[T] (System.Collections.Generic.IEnumerable`1[T] sequence, System.Action`1[T] action) [0x00014] in <2f5aaaa000594d07b9998f4cff1e9662>:0
at HarmonyLib.Harmony.PatchAll (System.Reflection.Assembly assembly) [0x00006] in <2f5aaaa000594d07b9998f4cff1e9662>:0
at KMod.UserMod2.OnLoad (HarmonyLib.Harmony harmony) [0x00007] in <990b4cf9a7d84305ad7eaef1059b672b>:0
at KMod.DLLLoader.LoadDLLs (KMod.Mod ownerMod, System.String harmonyId, System.String path, System.Boolean isDev) [0x00222] in <990b4cf9a7d84305ad7eaef1059b672b>:0

at UnityEngine.Debug.LogError (System.Object message, UnityEngine.Object context) [0x00000] in <72b60a3dd8cd4f12a155b761a1af9144>:0
at Debug.LogError (System.Object obj, UnityEngine.Object context) [0x00000] in <0f4b778ef79c497e89f6ee18303840cf>:0
at DebugUtil.LogErrorArgs (UnityEngine.Object context, System.Object[] objs) [0x00000] in <0f4b778ef79c497e89f6ee18303840cf>:0
at DebugUtil.LogException (UnityEngine.Object context, System.String errorMessage, System.Exception e) [0x00000] in <0f4b778ef79c497e89f6ee18303840cf>:0
at KMod.DLLLoader.LoadDLLs (KMod.Mod ownerMod, System.String harmonyId, System.String path, System.Boolean isDev) [0x00000] in <990b4cf9a7d84305ad7eaef1059b672b>:0
at KMod.Mod.Load (KMod.Content content) [0x00000] in <990b4cf9a7d84305ad7eaef1059b672b>:0
at KMod.Manager.Load (KMod.Content content) [0x00000] in <990b4cf9a7d84305ad7eaef1059b672b>:0
at Global.Awake () [0x00000] in <990b4cf9a7d84305ad7eaef1059b672b>:0
at UnityEngine.Object.Internal_InstantiateSingleWithParent_Injected (UnityEngine.Object data, UnityEngine.Transform parent, UnityEngine.Vector3& pos, UnityEngine.Quaternion& rot) [0x00000] in <72b60a3dd8cd4f12a155b761a1af9144>:0
at UnityEngine.Object.Internal_InstantiateSingleWithParent (UnityEngine.Object data, UnityEngine.Transform parent, UnityEngine.Vector3 pos, UnityEngine.Quaternion rot) [0x00000] in <72b60a3dd8cd4f12a155b761a1af9144>:0
at UnityEngine.Object.Instantiate (UnityEngine.Object original, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation, UnityEngine.Transform parent) [0x00000] in <72b60a3dd8cd4f12a155b761a1af9144>:0
at UnityEngine.Object.Instantiate[T] (T original, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation, UnityEngine.Transform parent) [0x00000] in <72b60a3dd8cd4f12a155b761a1af9144>:0
at Util.KInstantiate (UnityEngine.GameObject original, UnityEngine.Vector3 position, UnityEngine.Quaternion rotation, UnityEngine.GameObject parent, System.String name, System.Boolean initialize_id, System.Int32 gameLayer) [0x00000] in <0f4b778ef79c497e89f6ee18303840cf>:0
at Util.KInstantiate (UnityEngine.GameObject original, UnityEngine.GameObject parent, System.String name) [0x00000] in <0f4b778ef79c497e89f6ee18303840cf>:0
at LaunchInitializer.Update () [0x00000] in <990b4cf9a7d84305ad7eaef1059b672b>:0
Build: U47-561558-SD

Do you think this could be a mod conflict?

Yes, look like a mod conflict.
Some mod related to dupe movement or pathfinding , and it deeply changed the game.
Do you have any local mod?(not installed from steam workshop)

No I do not - this is my mod list (though not all of them are active due to issues popping up on startup):
Stairs (not active)
Queue for Sinks (not active)
Pip Plant Overlay
BottlesToPipes
Blueprints fixed
Buildable Dirt Tile
Insulated Door
Airlock Door
Wounded Go To Med Bed
Drains
Build Over Plants
CustomTemperatureOverlay
Giant Doors
Thermal Tooltips
Bigger Camera Zoom Out
Decor Lights
Wallpaper
GasOverlay
ChainedDeconstruction
Wall Pumps and Vents
Geyser Calculated Average Output Tooltip

Have no clue which one is causing conflict.
My suggestion is, reinstall this mod (unsubscribe from workshop ,launch the game , exit then resubscribe) and see if this help , try disable some of your mods and see if it fix until you found the one causing the problem.
I have noticed your game version is U47-561558-SD, which means you have enable debug mode. Probably nothing but it's better to disable, so we can prove it has no effect.

I feel like such an idiot - I was sure I had uninstalled and reinstalled the mod but it looks as if the issue came about between your mod and the Queue for Sinks mod.. I uninstalled and reinstalled both and suddenly they both started working. Thanks for the assist as these two mods are on top of my list for what they add to my game. Keep up the great work, and thanks for the assist! :)

No problem.