Hi!
I recently encountered a strange error. I was playing Roblox (Sober) and suddenly my clicks weren’t registering, but my mouse movements were. I restarted and it was fixed, but since then, when I use a browser or the terminal, it starts clicking and selecting letters in a strange way.
I’m using Manjaro26-GNOME.
Does anyone know of a solution?
Hi @k14 and welcome to the Manjaro community! 
It may well help if you provide some system information, i.e. in a Terminal window, run
inxi -zv8
… copy the whole output, then paste here, select the pasted text and click the </> button at the top of the Reply window; this makes it more Forum-Friendly™ by creating a scroll-able text box rather than an elongated post.
Note that privacy-sensitive information (MAC addresses etc.) are filtered using that command.
Once we know something about the system you are running, it will provide better avenues for those able to help. 
Your mouse is worn out - I have had similar experiences when the plastic that make up the mouse button sudden gets ‘tired’ - with a general misbehaving as result.
It’s probably the mouse, if you have another (known working) mouse then see if that one is also affected.
Could be that, or the switches starting to fail, or a combination of the two.
If the switches are failing then you may also get multiple clicks instead of a single click, and ghost clicks.
I’m well acquainted with worn mouse buttons and with one I frequently have to make several attempts to select text, due to the contact opening mid-drag.
I would have recommended switch-cleaner but have found this to make things worse in one case, so use when there’s nothing to lose.
What exactly do I need to copy, the connected peripherals?
I’m slightly confused as to the last part of your reply, but I just meant run the inxi command in a Terminal, select all the text there then copy and paste it here. Hope this helps.