Malfunctioning enzyme is most likely an inaccurate term. What I mean is disrupted 5ar2 enzyme function. This can in theory happen in more than one ways but the evidence points towards lack of gene expression of the gene encoding for 5ar2 (SRD5A2), which essentially means the enzyme is not produced in the affected cells.
At the tissue level, some cells may still be producing the enzyme, so the enzyme will not be completely absent from the tissue but will be highly reduced in concentration (and, in many people, more so than during regular Finasteride administration).
I have no idea how this specifically happens at the sub-cellular level or what all the different ways it could happen are but all evidence indicates, in my opinion, that it happens as a response to sufficiently low or rapidly falling DHT levels, which admittedly seems paradoxical.
The evidence in support of this theory is that people can get PFS from a single Finasteride pill, without any prior exposure. The reason I believe these reports is because I myself got PFS from a single pill. It happened within 20 minutes of taking the pill so there is no doubt it happened during a phase of falling DHT.
Note that this theory is in contravention to the dominant theory of PFS, which argues that genes are methylated in PFS as a response to rising DHT levels after cessation of Finasteride treatment in an environment of upregulated androgen receptor (AR) from prior finasteride use.
The dominant theory, in my opinion, cannot explain my experience and the experience of many others who got PFS from a single pill. It can also not explain, in my opinion, the experience of people who got PFS while they were on Finasteride.
The dominant theory can only explain, to my knowledge, the experience of people who get PFS only after stopping Finasteride. I believe, however, that this is a separate type of PFS (what I have dubbed PFS type 1), which is not caused by methylated genes (and is therefore less permanent) but by the state of AR upregulation coupled with an HPTA axis hormonal crash after stopping Finasteride. This, of course, is speculative.
Likewise, the dominant theory would predict that PFS can in theory be begotten from extremely high levels of androgens from steroid abuse when AR are overwhelmed, even without prior finasteride use or AR upregulation. This does not happen to my knowledge.