I'm also having this problem. Post your mod list and I'll post mine, maybe there's something in common that makes sense.

This also happens to be my load order:

Harmony
Core
Royalty
SRTS Expanded
Jecs Tools (Unofficial)
Two's Tilled Soil - 120%
Defensive Machine Gun Turret Pack
Animals Logic
Realistic Rooms
RimHud
Just Ignore Me Passing
Tech Advancing
Replace Stuff
Recipe Icons
Wall Light
Misc. Training
Interaction Bubbles
A Dog Said... Animal Prosthetics
Mend and Recycle
Expaded Prosthetics and Organ Engineering
Rimfridge
Trading Spot
Quality Builder
HugsLib
Mad Skills
Xeva's Rimhair
RT Fuse
EdB Prepare Carefully
Dubs Mint Menus
Allow Tool
Where is my weapon?
Mortar Accuracy
Sparking Worlds - Full Mod
Snap Out!
Pick Up and Haul (Continued)
Doors Expanded (Dev)
Runtime GC
Smarter Construction
Level Up!
RunAndGun
StackXXL
Go Explore!
Better Traders
Vanilla Expanded Framework
Vanilla Expanded - Royalty Patches
Vanilla Events Expanded
Vanilla Fishing Expanded
Ed - Embrasures
Vanilla Furniture Expanded
Vanilla Furniture Expanded - Production
Vanilla Furniture Expanded - Security
Biomes! Core
Biomes! Islands
Loading In Progress

I have same issue, it started when I was tryieng new mod, that make more mechanoid enemies. firstly I was thinking its mech mod, but it's acually this mod itself. I informes creator, but there is maybe more in it, becose it's long time like that

do you have mods that influence projectile speed? because too fast projectiles (mosatly through other mods) will piece the shield more often

why?

how does shield-code work:

it rapidely scans inside the shield radius for projectiles and their vectors and then deletes incoming ones.

if your modded projectile speed is too fast, it will arrive (maybe instant) before it can be scanned and therefore stopped.

ps: its nothing the mod author can do anything about since its the way all shields inside rimwork work.

oh yeah
i do have that

That was the issue, thank you very much Prester. I tested it and eaven 20 lancers was unable to pass throu them, If someone want badly bigger speed of projetiles, max speed with minimal issue is 150%

can I ask about the shield code scaning, if the shield radius is bigger, it takes little bit more time than shiled radius with small reach? maybe that's why original shields for mechs and low shield pack had only small issue or no issue to block projetile. maybe that's why we thought that mod is broken