Solved (sort of)
Ok, so I have it up and working. The issue is with the setting https_login (Use HTTPS login) it needs to be set to encourage (Encourage secure (https) login).
Any other setting except for disable, will cause the above described error (rendering your website useless).
I also noted that if ever you choose: force, force_nocheck or allow, your website will be rendered unusable, and even after changing the setting back, will have no effect and the website will be non-recoverable.
This was a new install, so I didn't loose too much the first time, but it took me about 14 installs to get this figured out. If your upgrading from tiki 12.x be sure to have a database backup. Likewise, if you have an existing website on 14.x and enabling cloudflare ssl for the first time. Be use to keep good database backups!
My final settings were to keep the .thaccess settings ( I guess you only really need the two lines that redirect http to https, but for SEO you should choose ether https://www.mysite or https://mysite, the second two lines redirect all other traffic to the non-www url. An the only ssl setting I changed in tiki was the one in question above. I could perhaps enable others, but am not sure its worth the headache of reinstalling tiki if they don't work.
It should perhaps be mentioned that this is really not a very secure way of implementing ssl. not only the flexible ssl, but also having logins using https optional. Would be much better if tiki would decline any non-secure login attempts, and force data to be transmitted over ssl, or not at all. However in my case, this relatively insecure method of ssl, is good enough.
Hope this helps someone save some time, and perhaps not give up on tiki. Its a really wonderful platform most of the time