Ahem, an important necessary embarrassing reprise of some of my earlier words... blush. Previously as one part of my many tests over the past several days since this dumb new problem appeared out of nowhere, i definitely wanted to verify/discover if this fault occurred with not only my booted 4.17 kernel, so at that time i also tested my 4.16 kernel. The identical no-network post-Resume stupidity also manifested with this 4.16 kernel. Embarrassingly, in hindsight, i neglected to then also test my third installed kernel, 4.14. In this case it belatedly transpired that Meatloaf was wrong; Two Outa Three ARE Bad. Sigh, read on...
25/7/18: 11:11: UPDATE... I discovered that Kernel 4.14.56-1 DOES still happily Resume with normal network connectivity [why oh why lazily t'other day did i only test the two later kernels?]. Kernels 4.17.7-1 & 4.16.18-1 continue with their crazy recent problem of no network post-Resume... despite my Tower having successfully run with both the 4.17 & 4.16 series for several months, ever since they stopped being RC. What broke just recently?
11:45: Final reboot for today [???] after performing the latest Stable Update 2018-07-24 [which upgraded two of my three kernels], then repeated the Suspend-Resume tests. The new 4.17.9-1 still cannot reconnect to the network post-Resume. The new 4.14.57-1 still DOES reconnect to the network post-Resume.
So, now after 3.5 days of frustrating time-stealing shenanigans, Tower once more has network post-Resume [but ONLY if i run the 4.14 kernel]. Since my migration to Manjaro last year, this had never ever ever been a problem, regardless of what kernel i used... until something went down the toilet on 22/7. Weird.
Agreed, & i always strive for just this [me be a retired machinery diagnostics engineer who earned her daily bread doing logical troubleshooting diagnostics, so it's kinda habitual]. I won't bore you with details now, but none of the items you suggested here are applicable atm... various other tests & actions i did over the past several days [but was too lazy to document here] eliminated all of those. Thanks all the same.
Teehee, you got it in one! This is part of the reason i know that the weird recent fault is not my modem-router or upstream, but is restricted to my Terrorised Tower... both my Android phone & my Manjaro KDE Lappy have continued to have no problems connecting to my modem-router & hence internet anytime i want [including post-Resume in the case of Lappy]. Sigh.
Ha, machines were easy in comparison. They simply followed the laws of physics, thermodynamics, tribology & kinematics. Computers on the other hand seem to have a mind entirely their own, & obey nothing but voodoo black magic!