I died after I had gotten the message that it was active.

Dedicated Crafty Server running on Linux (Debian 11 -> CasaOS -> Crafty)
Mc 1.21.1
Neoforge 21.1.172
Ars Nouveau 5.10.3

Modified Create Live 6 Modpack

Server-Side Mod list:
Architectury 13.0.8 (architectury)
Ars Creo 5.1.0 (ars_creo)
Ars Elemental 0.7.5.0.1 (ars_elemental)
Ars Monde Lib 0.3 (ars_monde_lib)
Ars Nouveau 5.10.3 (ars_nouveau)
Ars Nouveau's Flavors & Delight 2.1.8 (arsdelight)
Ars Technica 2.3.0 (ars_technica)
Backpacked 3.0.0-beta.12 (backpacked)
BadOptimizations 2.3.0 (badoptimizations)
Balm 21.0.48 (balm)
chunksending mod 2.8 (chunksending)
Chunky 1.4.23 (chunky)
Cloth Config v15 API 15.0.140 (cloth_config)
Clumps 19.0.0.1 (clumps)
Common Networking 1.0.18-1.21.1 (commonnetworking)
conditional mixin 0.6.4 (conditional_mixin)
Controlling 19.0.5 (controlling)
CorgiLib 5.0.0.4 (corgilib)
Crafting On A Stick 1.21.0.2 (crafting_on_a_stick)
Create 6.0.6 (create)
Create Ars Nouveau Compat 0.0NONE (create_ars_nouveau_compat)
Create Chocolate Fountain 1.21.1-1.0.0 (create_chocolate_fountain)
Create Compressed 2.2.0 (create_compressed)
Create Encased 1.7.1-fix2 (createcasing)
Create Factory Abstractions 1.4.5 (create_factory_abstractions)
Create Factory Logistics 1.4.5 (create_factory_logistics)
Create Liquid Fuel 2.1.1-1.21.1 (createliquidfuel)
Create More Chocolate 3.4.0-1.21.1 (create_chocolate)
Create Oh The Biomes We ve Gone Compat 0.0NONE (create_otbwg_compat)
Create Railways Navigator 1.21.1-beta-0.8.4 (createrailwaysnavigator)
Create Stuff 'N Additions 2.1.0. (create_sa)
Create: Central Kitchen 2.1.3 (create_central_kitchen)
Create: Connected 1.1.5-mc1.21.1 (create_connected)
Create: Deep Dark 1.9.0 (create_deep_dark)
Create: Dragons Plus 1.6.1 (create_dragons_plus)
Create: Food 2.0.0 (createfood)
Create: Pattern Schematics 2.0.9 (create_pattern_schematics)
Create: Trading Floor 3.0.9 (trading_floor)
Create: Vibrant Vaults 0.3.2 (create_vibrant_vaults)
Cupboard mod 2.9 (cupboard)
Curios API 9.5.1+1.21.1 (curios)
DragonLib 1.21.1-2.2.24 (dragonlib)
Entity Texture Features 6.2.9 (entity_texture_features)
EntityCulling 1.8.0 (entityculling)
Farmer's Delight 1.2.8 (farmersdelight)
FastLeafDecay 35 (fastleafdecay)
Ferrite Core 7.0.2 (ferritecore)
Flywheel 1.0.4 (flywheel)
Forge Config API Port 21.1.1 (forgeconfigapiport)
Forgified Fabric API Base 0.4.42+d1308ded19 (fabric_api_base)
Forgified Fabric BlockView API (v2) 1.0.10+9afaaf8c19 (fabric_block_view_api_v2)
Forgified Fabric Renderer API (v1) 3.4.0+9c40919e19 (fabric_renderer_api_v1)
Forgified Fabric Rendering Data Attachment (v1) 0.3.48+73761d2e19 (fabric_rendering_data_attachment_v1)
Framework 0.9.6 (framework)
FTB Chunks 2101.1.9 (ftbchunks)
FTB Library 2101.1.14 (ftblibrary)
FTB Quests 2101.1.10 (ftbquests)
FTB Teams 2101.1.2 (ftbteams)
Fusion 1.2.7+b (fusion)
GeckoLib 4 4.7.6 (geckolib)
Gravestone Mod 1.21.1-1.0.24 (gravestone)
Incendium 5.4.3 (incendium)
Jade 15.10.1+neoforge (jade)
Jade Addons 6.1.0+neoforge (jadeaddons)
Journeymap 1.21.1-6.0.0-beta.52 (journeymap)
JourneyMap API 2.0.0 (journeymap_api)
Just Enough Items 19.21.0.247 (jei)
Konkrete 1.9.9 (konkrete)
KubeJS 2101.7.1-build.181 (kubejs)
KumaAPI 21.0.5 (kuma_api)
L2Core 3.0.8+1 (l2core)
Lithium 0.15.0+mc1.21.1 (lithium)
Melody 1.0.10 (melody)
MidnightLib 1.6.9 (midnightlib)
Minecraft 1.21.1 (minecraft)
MmmMmmMmmMmm 1.21-2.0.8 (dummmmmmy)
Model Gap Fix 1.21-1.10 (modelfix)
ModernFix 5.24.3+mc1.21.1 (modernfix)
Moonlight Lib 1.21-2.19.1 (moonlight)
Mouse Tweaks 2.26.1 (mousetweaks)
Nature's Compass 1.21.1-3.0.2-neoforge (naturescompass)
NeoForge 21.1.172 (neoforge)
No Chat Reports 1.21.1-v2.9.1 (nochatreports)
Noisium 2.3.0+mc1.21-1.21.1 (noisium)
Not Enough Crashes 4.4.9+1.21.1 (notenoughcrashes)
Nuggets 1.0.10.41 (nuggets)
Oh The Biomes We've Gone 2.3.13 (biomeswevegone)
Oh The Trees You'll Grow 5.0.14 (ohthetreesyoullgrow)
Ok Zoomer 10.0.0-beta.10 (ok_zoomer)
OpenLoader 21.1.5 (openloader)
PacketFixer 3.1.4 (packetfixer)
Plasmo Voice 2.1.4 (plasmovoice)
Ponder 1.0.56 (ponder)
PortalGems 1.0.1 (portalgems)
PrickleMC 21.1.8 (prickle)
pv-addon-groups 1.1.0 (pv_addon_groups)
Rechiseled 1.1.6+a (rechiseled)
Rechiseled: Create 1.0.2 (rechiseledcreate)
Reese's Sodium Options 1.8.3+mc1.21.4 (reeses_sodium_options)
Rhino 2101.2.7-build.74 (rhino)
Saturn 0.1.5 (saturn)
Searchables 1.0.2 (searchables)
Smoothchunk mod 4.1 (smoothchunk)
Sodium 0.6.13+mc1.21.1 (sodium)
Sodium Extras 1.0.7 (sodiumextras)
Sodium Options API 1.0.10 (sodiumoptionsapi)
spark 1.10.124 (spark)
Starbunclemania 1.4.0.1 (starbunclemania)
SuperMartijn642's Config Library 1.1.8 (supermartijn642configlib)
SuperMartijn642's Core Lib 1.1.18+a (supermartijn642corelib)
TerraBlender 4.1.0.8 (terrablender)
Too Fast 0.4.3.5 (toofast)
TRansition 1.0.2 (transition)
TrashSlot 21.1.4 (trashslot)
TRender 1.0.4 (trender)
Visuality: Reforged 2.0.5 (visuality)
Wrench Wrapper 0.6.2 (wrench_wrapper)
Yeetus Experimentus 87.0.0 (yeetusexperimentus)

Which armor were you using? Was it an addon armor? I cannot recreate this issue. I was able to die, trigger the undying, sleep, then trigger it again immediately after.

I didn't mean to close the issue, my hand slipped while typing on my phone :/

I had the thread on the tier 3 slot of the tier 2 armor from Ars Nouveau. It was the variant that was balanced in armor and slot power, I don't remember the exact name right now. It never worked even though I slept multiple times and got the message that says it is recharged every time.