Please provide system information as described (below) and also note the Moderation comment in your first post.
The links given (also below) will help you use the forum more effectively. It is expected that you follow them and use the practical information found to help attract quality responses.
With regard your issue, the following link might give some background as to why some of these issues with m,ultiple monitors on HDMI can occur;
If your issue doesn’t strictly fall under that scenario, I’m sure someone can help further when they are able.
Regards.
Welcome to the Manjaro community
As a new or infrequent forum user, please take some time to familiarise yourself with Forum requirements, and the many ways to use the forum to your benefit:
Update Announcements
The Update Announcements contain important information and a Known Issues and Solutions section that should generally be checked before posting a request for support.
System Information
While information from *-fetch type apps might be fine for someone wishing to buy your computer, for Support purposes it’s better to ask your system directly; 
Output of the inxi command (with appropriate parameters, and formatted according to forum guidelines) will generate information that may be useful for those wishing to help:
inxi --filter --verbosity=8
or the short form:
inxi -zv8c0
- inxi man pages (Arch Manual)
Be prepared to provide output from other commands whenever asked. It’s equally important to provide as much actionable information as possible in your first post, rather than simply indicating there is a problem.