Does firmware version impact iRule functionality?

Hi, 

you need to do two exercises : 

• have a look in v16.1.3.5 (it should be that not "16.3.1.5") release Notes and search by irule , you can see if there are new changes in it or not.
  • https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/releasenotes/related/relnote-supplement-bigip-16-1-3-5.html
• also have a look in F5 Bug tracker and select your version , then search for irule to see if there are bugs and all workarounds :
  • https://my.f5.com/manage/s/bug-tracker

Thanks