Necroing this topic, since the issue still plagues us...
I tried a straight copy of textual links, replacing the 'zerothread' bits with the proper phpBB3 syntax, and while that does lead to links working, the thread numbers do not seem to align with the topics they are supposed to...
Reading thru the above, seems there was a patch that worked at one point in time, and though I imagine the DB might be relatively large, actual member traffic would seem to be light enough that any reasonable hosting service should be providing the hardware needed for phpBB to run at decent speed...
Anyway - I've been running forums for years
(of several different software flavors incl phpBB since v1 & up to v3, but prefer Simplemachines... ), and gladly offer my help in getting this fixed. Be glad to show proof of identity and a "CV" prior to any possible security/privacy/etc issues.
If an Admin doesn't see this, or come by often anymore, would someone forward them a link to this reply? Thanks!