Let us start with Premiere Elements 13 on what computer operating system and have you updated 13 to 13.1 yet using an opened project's Help Menu/Updates.
To your immediate issue...
1. What are the properties of your source video...
interlaced or progressive
pixel aspect ratio
Are you sure you are still not recording with a variable frame rate?
2. Companion question for "1", what is your project preset which is supposed to be matching the properties of your source file?
The above is just the preface for those export settings. Are you sure that none of the project settings or the recordings have unknowingly changed? Who is setting the project preset, you or the project? If the project, then check out Edit Menu/Project Settings/General to assure that the project did not give you the wrong project preset this time. Then you set the project preset manually (File Menu/New/Project - Change Settings). Details to follow if necessary.
AVCHD is a choice under Publish+Share/Computer/. It is not one of the presets under Presets. What are you selecting for the Presets field - MP4 H.264 1920 x 1080p30 or something else? I would suggest considering increasing the bitrate under the advanced export settings but you already have a file size of about 2 GB with your present target and maximum bitrates. But you can do a mini test run to determine if increasing the bitrate would give you the quality, if not the file size, that you seek.
Further details to follow based on the details in your reply.
Any questions or need clarification, please do not hesitate to ask.
Here's a MediaInfo xml file from the source video from above.
I setup the preset, and no, no else uses my computer, I live alone.
The preset I setup under AVCHD was mp4 1920 x 1080 30 fps, then I defined the advanced optinos for the preset as
above. This normally creates a lovely video for YouTube, however this time it wouldn't.
As for project settings, I followed the Project Help in Project Settings, which said "If you specify lower-quality settings for output
(such as streaming web video), do not change your project settings. Change your export settings instead."
On Project settings once the project is created (as this is) there is no way to change any of it's settings in the Project
Settings menu as all options are greyed out, except for Maximum Bitdepgth which I did not have ticked.
So I set it all during export. ie I like a 30 min vid to be around 2Gb which is nice for Youtube.
Normally my bit depth on export is 8/11 but after such poor quality I increased it to 11/13 and the
quality was no better. This is when I decided to post a question as increasing the bit depth had no effect.
So then I increased the exported bit depth to to 13.86 / 15.36, and the quality did nott improve not one jot!
It's puzzling since the last episode was great and was build from the exact same source video. It was an hour
long and I only needed 30 mins, so it's made two episodes. First was great quality, but this is really bad.
I'm stumped, because nothing has changed on my system, or in APE settings.
Hope you can help.