It's damaging in normal circumstances, but in the times of pandemic any court would see this delay as justified, and IRCC can get away with it. 4/6 and 3/5 says nothing really about IRCC intentions to make it harder on applicants, as all the delays happened after the application is submitted. Also, take for example, selecting PR cards to be picked up from offices, although they are closed. Why would they select someone who meets the requirements to collect their card from the office in times of the pandemic? I want to emphasize this is a hypothesis, but I think it's plausible giving the current trends.
I think most 2019 applicants are worst than 2020 and later applicants in all offices. IRCC seems to be under internal pressure to meet some targets for each year, but once that's met, the remaining applications are tossed to collect dust.
It's a possibility. None of us know exactly what's going on inside IRCC offices. If you've been around, you know the bureaucracy can get a little protectionist here. And secrets can stay much longer in such environments. (I was, in fact surprised to see only Canadian persons can file ATIP requests.)
It's certainly strange, some of these cases - one 2018 or 19 case where the wife failed the test and the IRCC couldn't find another other slot for her ever since?! And recently, the husband was trying to separate his + kid's application from his wife's and the split request was denied. Things like these are borderline inhuman. And there are others where 2019 cases are sporadically getting new updates after seeing no action for several months. Certainly difficult to explain those. Apparently its the same with cobie2.
I wouldn't listen to anyone on whether or not to file mandamus, unless they've filed one themselves. If your own deadline says its time to go for the next step, you should start the consultation and ignore everyone else. If I'm filing, I'd also pick a media-savvy lawyer if possible, just an add-on. Make sure to look for all the signs: fixed fee that's preferably publicly posted (or pro bono is much better if available.
In the US, the federal government is supposed to pay the suing attorney if the government loses, so many lawyers take immigration cases pro bono even for folks that can't otherwise afford it. The government pays the attorney fee if the government loses, no one pays if the government wins. Not sure if Canada has a similar provision, I'd check that. Insist on a proper budget in all plausible scenarios - even if the case drags on etc, don't make them think you have an unlimited budget. Once you find a fitting attorney, you have someone who knows the system better and whose incentives are 100% aligned with yours. I don't think you're interested in money, but folks asking for money or damages from IRCC are going to have a weaker case. The goal is to get the application processed not making some money out of this.
More importantly: I don't know if Canada has a system where you can access all federal dockets (US has a paid case docket system where you get free access for upto $25/qtr and they'll bill you some small amount after that - or sites like casetext). If there's one, I'd equip myself with the case law - EVEN BEFORE going to an attorney. It might sound complicated and also a bit of a dry reading but it's usually a simple description of the litigation scenario and the outcomes, again I don't know if there's transparent docket access in Canada.
Filing another application (as others have suggested) is not a bad idea but what's the guarantee that will work? Just like attempting to trigger a file transfer by moving, it's just another gamble. In a third-party forum like a mandamus proceeding, IRCC might say you are the one causing the delay by filing a duplicate application. (I still think moving is a slightly better option even though it's not an option for the vast majority.)
Basically you have two groups of options: one is to keep prodding IRCC to process your application (writing to legislators etc/filing a duplicate application/moving etc). The other option is you're done dealing with IRCC and are going to a third party forum like mandamus.
You decide based on what your situation demands. Irrespective, I'd read up on everything I find about mandamus cases - both in this fourm and on the internet.