Yeah.. I'm sure it has got something to do with taking 80mg of lope daily, and hopping on subs.. you would think it would be out of your system 2 days later.. that's just how it is though with subs. A lot of people have to wait for long amounts of time after taking any sort of full agonist or different opioid before jumping on bupe.. I myself have done massive amounts of dope, oxy, dilaudid, opana, etc... then taken bupe 12hrs to at the most 24 hrs later after any given opioid/opiate, and been fine every time.. never have I really gone into full blown PWD, because I have a very fast metabolism.. but that does have a lot to do with how soon/late you should wait before taking bupe, no matter the ROA after any other opioid.. the only one you can actually take with bupe, and not go into PWD (so I have heard at least, never actually tried this one I'm about to mention, just heard a lot about it..)is tramadol.. I have heard it actually potentiates the bupe, tremendously from others who have done this, I have never even met anyone who has tramadol though.. I only have ever had access to the stronger opis.. dope, oxy, dilaudid.. etc..
And I would give plugging another try with bupe, if your usual ROA is sublingual.. I know you said you tried every other ROA besides IV, including plugging and none worked at 4mg.. but tacodude is right, bupe seems to be much stronger IME at least, when taken at around 2mg doses each time.. 1-2mg is my usual dose I do at a time.. I slam my shit.. wish I never started but, I cant stop now.. solely just because I like IVing.. or not so much like, but have an addiction to and don't know how to make myself go back to sniffing or plugging it my bupe.. I just feel like I wont get the same efficacy as all the others have BAs lower than the 100% BA IV bupe has, also am just totally addicted to the ritual.. And the actual feeling I get, if I smoke weed and take benzos before I do the bupe.. its an incredible synergy, that has its own nice "opiate-esque" high.. very nice feeling, I have become a total stoner again now, as weed/THC makes bupe like 5x stronger feeling, as do the kpins I take daily as well, which I am prescribed with my bupe. I am in no way telling you OP, to go out and take klonopin every day, and shoot bupe! NO! do not.. benzos are for those who absolutely need them to function in this world properly, and no one else to take on a daily basis.. if you can keep the usage minimal they are great with bupe thought, but daily benzo usage leads nowhere good.. I have like 10/10 anxiety on a scale from 1-10 anxiety level.. and have tried so many other things like, SSRIs before I hopped on klonopin 5 years ago.. Weed however, is great with just bupe on its own too! If you aren't feeling it now, but aren't in PWD anymore.. Bupe is like the one opioid(well partial agonist opioid..) that I never seem to gain a tolerance too, only throughout the course of a day.. like if I do too many shots of it too close together, it does not work as well at all.. but if I wait longer than 6 hours for each 2mg shot of bupe I take, I am golden.. especially with some herb!
So yeah, not sure if its just you... maybe you do have some kind of crazy tolerance built up to it, even though I have never really had this happen with bupe.. and its the only thing opioid related that this hasn't happened to me with.. oxy my tolerance got worse, with each pill I did/took but bupe, seems to always be around the same kind of potency and have the same feeling for me at doses 2mg or less, when either plugged or IVed for me.. sometimes I used to sniff it too, though plugging is better for you than sniffing is, overall.. and MUCH better than IV, plugging is truly the least harmful ROA if you think about it... from an HR stand point, if done correctly and with the proper tools, plugging is safe, and harmless(as far as I know) to your body.
And also I have very limited experience with loperamide.. so I cant really say, anything about that too much.. but I do know, it can definitely throw you into precipitated WDs, when taken too soon before bupe... for some. But everyone is very different when it comes to when they can take bupe after a full agonist opiate/opioid and be okay, with no PWDs and how long they have to wait between them both.. Good luck with the subs!