Issue:
You are seeing many of your Office documents opening up from SharePoint 2013 in a "Read-Only" state, but other files are opening in an "Online" state. This is sometimes shown as a hard limit in the size of the document being opened.
Example: Documents over 6MB in size are opening as "Read-Only", but documents smaller than that are opening normally.
Cause:
It is possible the FileWriteChunkSize property has been changed in the SharePoint 2013 Farm
Resolution:
1. Check the property size in SharePoint Management shell(Specify your own Web Application URL):
$webapp = Get-SPWebApplication http://sp2013
$webapp.WebService.FileWriteChunkSize | Write-Host
2. If the value shown is not equal to 64320 then proceed to step 3.
3. Reset to default value of 64320 in SharePoint Management shell:
$webapp.WebService.FileWriteChunkSize = 64320
$webapp.update()
NOTE:
SPWebApplication.WebService.FileWriteChunkSize shouldn't be modified from the original value. The value is used in the chunking algorithm and doesn't act as one would think, for example setting that value to be 1 GB doesn't cause the chunks to be 1 GB each and also doesn't cause SharePoint to start chunking at that 1 GB. The value should be left at its original state and not modified.