So, we are seeing a history; of wide ranging trouble codes, about communication and power, being killed off to various parts, modules and components, in the car. Probably, the top problems with see with these cars; is electrical related, they can be intermittent and hard to trace, find, nail down. :facepalm: :banghead:
Fixing these issues, will take time, effort and a process of elimination. I would be investigating things and you should be able to perform, a step by step process to narrow things down.
The basics, shouldn't be overlooked:
1. Visual inspections:
a. @ the battery: power connections, fuse box (damaged/melted?) and ground under the battery tray. VW issued, a service bulletin; for the grounds, for the coil pack, under the battery tray; actually, creating new ground wires and insuring, a intermittent ground issue was resolved.
https://www.youtube.com/watch?v=FjGkFqdS52w
b. @ the ecu, fixing power issue and finding the source of the problem, not just bypassing it with a jumper wire. When you find the source of the power issue; it may end up fixing other problems, that are intermittently bringing the ecu communications down.
c. @ ignition switch: as noted visual inspections, replace all damaged wires, plugs, switch, etc. Many things are powered through the switch and a no start condition; is common, when these part are damaged.
e. the abs, rear hatch and other possible issues, can be checked out as well, you might focus, on those later and work through the ecu, no comm and start issues to begin with. We can work on those; once, you get the car running correctly.
2. VCDS, can be very helpful at times; it may take some time, effort to look up output testng or live data capabilities, e.g. seeing if the bus is "up", etc. but I have found it helpful, when used correctly. In your case, you seem to have the VCDS "Lite", which may limit your ability to use the advanced features.
http://wiki.ross-tech.com/wiki/index.php/Functions
So, this was a bit of rambling here but I hope it makes some sense. The common thread, seems to be communications, power and connectivity issues, going down. All of the evidence and codes; that you have shared, ALL point, to strong possibility of wiring/harness/plug issues (power, grounds, wires, etc). The wide range of codes, can be confusing but realize, when you have power/charging and/or wiring issues, a bunch of codes can be thrown.
It MAYBE, a case, where you have multiple electrical issues; going on at once and thus, the odd, various trouble codes. Recently, we had a long no start thread with a crank sensor code; it took awhile, to work through each issue. In that case, it was possible (three) different problems; were contributing to it, (bad wiring to the sensor, bad ground wire, bad coil pack). SO, that was a tough one but taking, each possible issue at a time, we worked through it and finally, got the car running right.
There is no magic here: troubleshooting electrical issues is hard work, you have to visually inspect, follow wiring diagrams, test, diagnose and work through the problem, a process of elimination. I don't know, if this helps but you have your work cut out for you. If you are up to the challenge; we are here to encourage you and try to guide things, give back/forth questions, attempt answers, in your process of elimination.