Odoo 11 Qweb headers missing in PDF reports - odoo

Question

Using Odoo 11 with wkhtmltopdf verion 0.12.1.3
All the default headers are not on any of the PDF reports I print, even when I try to preview the document templates in general settings.
I still have the footers though.
Furthermore the reports are very plain now, like the table-striped that has become a white plain column, or "row" that doesn't show the elements inside in a row but rather one under the other.
Edit :
To illustrate my problem here is what happen when I chose the Standard template in General Settings and I try to Preview the document.
There is what happends
What's strange is that I didn't touch - I don't think so - this header in any way (even though I've done some custom reports but unrelated).
Here is the code of web.external_layout_standard:
<?xml version="1.0"?>
<t t-name="web.external_layout_standard">
<div class="header">
<div class="row">
<div class="col-xs-3 mb4">
<img t-if="company.logo" t-att-src="'data:image/png;base64,%s' % to_text(company.logo)" style="max-height: 45px;"/>
</div>
<div class="col-xs-9 text-right" style="margin-top:22px;" t-field="company.report_header" name="moto"/>
</div>
<div t-if="company.logo or company.report_header" class="row zero_min_height">
<div class="col-xs-12">
<div style="border-bottom: 1px solid black;"/>
</div>
</div>
<div class="row">
<div class="col-xs-6" name="company_address">
<span t-field="company.partner_id" t-field-options="{"widget": "contact", "fields": ["address", "name"], "no_marker": true}" style="border-bottom: 1px solid black; display:inline-block;"/>
</div>
</div>
</div>
<div class="article o_report_layout_standard">
<t t-raw="0"/>
</div>
<div class="footer">
<div class="text-center" style="border-top: 1px solid black;">
<ul class="list-inline mb4">
<li t-if="company.phone">Phone: <span t-field="company.phone"/></li>
<li t-if="company.email">Email: <span t-field="company.email"/></li>
<li t-if="company.website">Web: <span t-field="company.website"/></li>
<li t-if="company.vat"><t t-esc="company.country_id.vat_label or 'TIN'"/>: <span t-field="company.vat"/></li>
</ul>
<div name="financial_infos">
<span t-field="company.report_footer"/>
</div>
<div class="text-muted">
Page: <span class="page"/> / <span class="topage"/>
</div>
</div>
</div>
</t>
EDIT temporary SOLUTION
It might have been a cache problem since we were several people working on the same admin account at the same time.
Thus I copied the database. Checked it worked well in my new database (eureka!). Erased the old one. And changed the name of the copy by the old name.
BUT! at some point it keeps despairing again. I'm doing qweb changes in custom reports so I don't touch the headers but maybe it's connected...

Answer 1

It seems that your pdf processor (wkthmltopdf) is not finding the proper CSS to form the reports. I solved this issue in Odoo 11 with the following steps:
Create a new system parameter report.url
For this go to Settings -> Parameters -> System and check if the parameter report.url exists. If not create it.
Set the value of report.url to http://127.0.0.1:8069 or http://0.0.0.0:8069
This is by the way the approach suggested by CZoellner. I have learnt more insight from the discussion on headers and CSS in reports at Odoo Help.