@swimboy Eureka! It turns out it was caused by AdBlock. I hope this works for anyone else reading this with the same issue. DavidB

@misterrr I have exactly the same problem - what was working fine is now broken. I use Opera One(version: 102.0.4880.46) (x86_64) with OS Mac 10.14.6 (Mojave), I've tried playing with the settings in Facebook without improvement. A quick test with Safari does not show the problem. I use AdBlocker. I tried disabling AdBlocker without benefit, but perhaps I need to close and reopen Opera when I test this? Grateful for any suggestions. DavidB

@leocg
I've altered the Opera 'Settings' to allow hardware acceleration and the problem has resolved itself.

There is a nearby option :
"Allow use of computer's dedicated GPU". This is currently OFF. Should it be ON?

I believe that I had turned off the hardware acceleration because it created problems for some websites (though I cannot immediately recall which ones). What are the relevant arguments?

@leocg Hardware acceleration is disabled. I'm not familiar with 'html5test.com' but it tells me that WEBGL and WEBGL2 are both ticked. The other link produces the following:

Graphics Feature Status
Canvas: Software only, hardware acceleration unavailable
Flash: Software only. Hardware acceleration disabled
Flash Stage3D: Software only. Hardware acceleration disabled
Flash Stage3D Baseline profile: Software only. Hardware acceleration disabled
Compositing: Software only. Hardware acceleration disabled
Metal: Disabled
Multiple Raster Threads: Enabled
Out-of-process Rasterization: Disabled
OpenGL: Disabled
Hardware Protected Video Decode: Disabled
Rasterization: Software only. Hardware acceleration disabled
Skia Renderer: Disabled
Video Decode: Software only. Hardware acceleration disabled
WebGL: Software only, hardware acceleration unavailable
WebGL2: Software only, hardware acceleration unavailable

Problems Detected for Hardware GPU
Gpu compositing has been disabled, either via blacklist, about:flags or the command line. The browser will fall back to software compositing and hardware acceleration will be unavailable.
Disabled Features: gpu_compositing
Log Messages
GpuProcessHost: The GPU process crashed!

Does this offer a clue?

@operaoperandi Thanks. That leaves "Mojave" or operator error! Can anyone try this with Mojave, just to twist the knife?

@leocg As my post mentions, I am on MacOS Mojave using Opera for Mac and I see the problem. You have confirmed that the problem is not in Opera for Windows. I have confirmed the problem is not in another browser (Safari). What we need, to avoid suggestions of operator error, is for someone using Opera in a MacOS to attempt to reproduce the problem.

Using Opera 71.0.3770.271 on MacOS Mojave
On the St Albans local newspaper website, I try to open a graphical display including a zoomable map. I get told I should use a modern browser! Safari works.
The website/page is https://www.hertsad.co.uk/news/herts-coronavirus-stats-show-mixed-picture-1-6892674.
Is there something I should do to make these displays visible?

This is what is shown in Safari:

@swimboy
(from the OP)

I think I have cracked it!

In Opera/Preferences/Privacy there is an on/off option (which I vaguely remember altering in the past 10 days):

   "Block ads and surf the web up to three times faster”

When I turned this off, Ridewithgps once again worked as expected.

Thanks for your interest; this thread can now be closed.

David

(from the OP)
Still no improvement on latest Opera download of version 66.0.3515.103 18/2/20

18/2/20
A week ago Ridewithgps.com was working fine. Yesterday it was broken. Their Support suggested trying another browser - Safari works fine.

I have Opera 66.0.3515.7 and MacOS X 10.14.6 (Mojave)

Can anyone confirm this symptom? Or suggest a fix?

I've tried re-booting.

TIA David