Did some test runs using Firefox, Edge and Internet Explorer.... test posts with FF and Edge... no problem with any of those browsers either.
For any real suggestions.... we need some info to base suggestions on. Which OS ( and version ), which browser and version that is being used.
Probably would be also good to find out what your internet connection download speed is also.... visit
Speedtest by Ookla - The Global Broadband Speed Test to get that... upload speed doesn't matter too much...
If this is on some version of Windows... open a command prompt with admin rights and test the hard drive for possible errors... at the command prompt type ( no quotes ) "chkdsk /f" ... when asked if you want to run on restart ... answer yes and then restart the computer. After that... again open the command prompt with admin rights and run "sfc /scannow" ... then restart the computer again. That covers the basics for checking for possible corruptions in the file system.
If you don't already have Malwarebytes installed and updated... do that next. This checks for malware that most other antivirus programs ignore.
Try using a different web browser than what you normally use.
I'll check back in later if time permits.