I have a villager with perfect trades, 1 potato for 1 emerald etc. I attempted to move him to a better place, since he was in a 1x1 but the moment I checked his trades again, it shot up to about 9 potatoes for an emerald. I labelled this as question since I'm not sure if its a feature or bug.
I checked the server and client config files but there's nothing there matching this issue.

Thank you and have a great day!

Can you please send me the contents of your server config?
Have you had the cheap trades in the trader or when the villager was in the world?
Was it more expensive when having the villager in the trader or in the world?

Client File:
[villager]
#The volume of every villager related sound in this mod
#Range: 0.0 ~ 1.0
volume = 1.0
#The location of the cycle trades button
#Allowed Values: TOP_LEFT, TOP_RIGHT, NONE
cycle_trades_button_location = "TOP_LEFT"
#If villagers should be able to be picked up by sneaking and right-clicking
sneak_pick_up = true

Server File:
[breeder]
#The time in ticks the breeder takes to create a new villager
#Range: > 20
breeding_time = 1200

[converter]
#The time in ticks the converter takes to convert a villager
#Range: > 20
converting_time = 6000

[farmer]
#Lower values mean faster growth
#Range: > 1
farm_speed = 10

[iron_farm]
#The time in ticks the iron farm takes to spawn a golem
#Range: > 201
spawn_time = 4800

[trader]
#The minimum amount of time in ticks the trader takes to restock
#Range: > 1
min_restock_time = 1200
#The maximum amount of time in ticks the trader takes to restock
#Range: > 2
max_restock_time = 3600

[auto_trader]
#The minimum amount of time in ticks the auto trader takes to restock
#Range: > 1
min_restock_time = 1200
#The maximum amount of time in ticks the auto trader takes to restock
#Range: > 2
max_restock_time = 3600
#The cooldown in ticks for the auto trader to do a trade
#Range: > 1
trade_cooldown = 20

[villager]
#If the trade cycling button should be enabled
trade_cycling = true
#If the villager reputation should be the same for every player
#This affects the prices of cured/converted villagers and the prices of the auto trader
universal_reputation = true
#How frequent a villager block should make a villager sound
#Lower values mean more frequent sounds
#Range: > 1
sound_amount = 20
#If villagers should make sounds while in the players inventory
inventory_sounds = true

[incubator]
#The speed at which the incubator ages the villagers
#Range: 1 ~ 1024
speed = 2

I had the villager outside of the trader, however I've just checked again and it seems the prices are gradually going lower. I can try and reproduce it with the trading block if you need.
I put the same villager in a trader, to see what would happen however it had the same trades. Does a trader stop prices from changing somehow?

Thank you for the quick response btw!

So it happened outside of the trader block?

Yep

Then it can't be a problem of this mod. It doesn't alter the vanilla villager behavior.
Maybe you hit the villager and lost reputation.