Files of size above 25 MB could not be uploaded

I'm afraid this is definitely a Support Request rather than an obvious problem with the Drupal module.

The issue you're having could be quite specific to your environment.

Making sure StreamMaxLength isn't too low would be one of the first things I'd recommend you check, but looks like you've done that already.

If you really want to know what's happening, it might help to look at the clamd logs which might be at /var/log/clamav/clamav.log or perhaps going into syslog?

If that doesn't help, you can perhaps use tcpdump or similar to capture the network traffic between Drupal and clamd when a scan fails, in order to see if there are any clues there.

It would be good if the module did a better job of "surfacing" errors if that's possible; for example if the daemon responds with an error message.

Not something I can work on right now, but if there's not already an issue for that in the module's queue it'd be good to file one.

Have you made sure the module is in verbose mode to try to capture as much detail as you can about what's going on?

zip files of size above 25 MB

Does this impact files larger than 25MB which are not zip/compressed?
I wonder whether the uncompressed size and memory usage during decompression has an impact.

I tried uploading 79.0 MB pptx file, but same error came for this also, as you can see in the attached screenshot "error.png".

Fixed the issue by updating StreamMaxLength, MaxScanSize and MaxFileSize. Following are the updated configurations :

clamconf -n
Checking configuration files in /etc

Config file: clamd.d/scan.conf
------------------------------
LogSyslog = "yes"
TCPSocket = "3310"
TCPAddr = "127.0.0.1"
StreamMaxLength = "115343360"
User = "clamscan"
MaxScanSize = "115343360"
MaxFileSize = "115343360"

Automatically closed - issue fixed for 2 weeks with no activity.