What version of the game you are experiencing the issue with:
Live/Retail,

Describe the bug
Addon Crashing on Startup.
673x NeatPlates/NeatPlatesCore.lua:1955: attempt to call field 'SetSubText' (a nil value)
[string "@NeatPlates/NeatPlatesCore.lua"]:1955: in function <NeatPlates/NeatPlatesCore.lua:1953>
[string "@NeatPlates/NeatPlatesCore.lua"]:654: in function <NeatPlates/NeatPlatesCore.lua:642>
[string "@NeatPlates/NeatPlatesCore.lua"]:678: in function <NeatPlates/NeatPlatesCore.lua:665>
[string "@NeatPlates/NeatPlatesCore.lua"]:810: in function <NeatPlates/NeatPlatesCore.lua:800>
[string "@NeatPlates/NeatPlatesCore.lua"]:380: in function <NeatPlates/NeatPlatesCore.lua:353>

Locals:
index = nil
unitSubtext = nil
unitPlateStyle = nil
(*temporary) = nil
(*temporary) =

{
guid = "Creature-0-3024-2444-152-199220-0005BBCB38"
isMouseover = false
class = ""
rawName = "Violetwing Stagbeetle"
level = 1
red = 1
levelcolorRed = 0.500000
isDangerous = false
isPet = false
name = "Violetwing Stagbeetle"
pvpname = "Violetwing Stagbeetle"
levelcolorBlue = 0.500000
isBoss = false
isFocus = false
healthmax = 5
isTarget = false
levelcolorGreen = 0.500000
isMarked = false
alphaMult = 0.996078
isTapped = false
type = "NPC"
blue = 0
power = 0
isInCombat = false
threatSituation = "LOW"
powermax = 0
isTrivial = true
health = 5
showName = true
reaction = "NEUTRAL"
green = 1
isCasting = false
threatValue = 0
unitid = "nameplate1"
isMini = false
}
(*temporary) = "attempt to call field 'SetSubText' (a nil value)"
style = {
powerbar = {
}
spellicon = {
}
extrabar = {
}
target = {
}
spelltarget = {
}
healthbar = {
}
healthborder = {
}
targetindicator_arrowright = {
}
mouseover = {
}
durationtext = {
}
name = {
}
hitbox = {
}
raidicon = {
}
customtext = {
}
targetindicator = {
}
eliteicon = {
}
extratext = {
}
spelltext = {
}
extraborder = {
}
threatcolor = {
}
targetindicator_arrowtop = {
}
castbar = {
}
highlight = {
}
threatborder = {
}
skullicon = {
}
focus = {
}
targetindicator_arrowsides = {
}
targetindicator_arrowleft = {
}
castborder = {
}
subtext = {
}
level = {
}
frame = {
}
rangeindicator = {
}
castnostop = {
}
}
activetheme = {
powerbar = {
}
spellicon = {
}
extrabar = {
}
target = {
}
spelltarget = {
}
healthbar = {
}
healthborder = {
}
targetindicator_arrowright = {
}
mouseover = {
}
durationtext = {
}
name = {
}
hitbox = {
}
raidicon = {
}
customtext = {
}
targetindicator = {
}
eliteicon = {
}
extratext = {
}
spelltext = {
}
extraborder = {
}
threatcolor = {
}
targetindicator_arrowtop = {
}
castbar = {
}
highlight = {
}
threatborder = {
}
skullicon = {
}
focus = {
}
targetindicator_arrowsides = {
}
targetindicator_arrowleft = {
}
castborder = {
}
subtext = {
}
level = {
}
frame = {
}
rangeindicator = {
}
castnostop = {
}
}
unit = {
guid = "Creature-0-3024-2444-152-199220-0005BBCB38"
isMouseover = false
class = ""
rawName = "Violetwing Stagbeetle"
level = 1
red = 1
levelcolorRed = 0.500000
isDangerous = false
isPet = false
name = "Violetwing Stagbeetle"
pvpname = "Violetwing Stagbeetle"
levelcolorBlue = 0.500000
isBoss = false
isFocus = false
healthmax = 5
isTarget = false
levelcolorGreen = 0.500000
isMarked = false
alphaMult = 0.996078
isTapped = false
type = "NPC"
blue = 0
power = 0
isInCombat = false
threatSituation = "LOW"
powermax = 0
isTrivial = true
health = 5
showName = true
reaction = "NEUTRAL"
green = 1
isCasting = false
threatValue = 0
unitid = "nameplate1"
isMini = false
}
extended = Frame {
stylename = ""
requestedAlpha = 0
unitcache = {
}
widgetParent = Frame {
}
widgets = {
}
regions = {
}
Active = true
stylecache = {
}
style = {
}
unit = {
}
bars = {
}
defaultLevel = 20
visual = {
}
}
carrier = NeatPlatesCarrier-1 {
}
anchorgroup = {
1 = "healthborder"
2 = "threatborder"
3 = "castborder"
4 = "castnostop"
5 = "name"
6 = "subtext"
7 = "extraborder"
8 = "extratext"
9 = "spelltext"
10 = "spelltarget"
11 = "durationtext"
12 = "customt

Blizzard seems to have finally removed a lot of deprecated functions that the addon was still using.

Seems most of them are simple name changes to get it working again, but for buffs and debuffs its not a one to one replacement. So I'll look at it later today when I have more time.

Also experiencing this - addon is mostly ok until you are around mobs, then the error count starts climbing by about 100/s

Nameplates don't appear at all.

This appears to have begun within the last 24h or so.

Just a few quick fixes to at least have nameplates and no error spam:

NeatPlatesPanel.lua L13:
local version = C_AddOns.GetAddOnMetadata("NeatPlates", "version")

Hub.lua L574-575:
local TPCEnabled = C_AddOns.GetAddOnEnableState(player, "TidyPlatesContinued") ~= 0
local TPCHubEnabled = C_AddOns.GetAddOnEnableState(player, "TidyPlatesContinuedHub") ~= 0

AuraWidget.lua L11:
local _UnitAura = C_UnitAuras.GetAuraDataByIndex

TotemIconWidget.lua L14:
local name, _, icon = C_Spell.GetSpellInfo(spellid)

After looking a bit at the new aura structure I noticed Blizzard had a method in their AuraUtils that let me convert to new aura structure to the old one, so there were not changes necessary. For now at least...

I've fixed the other issues as well and pushed a release to curseforge.