3.1.13 seems to cause PHP timeout

Great plugin! Thank you for the hard work, it does not go un-noticed.

It seems having upgraded to 3.1.13 from 3.1.08 the download pages that seem to have a lot of downloads (400+) in a JS table seem to timeout and not show any downloads.

I found the only way to solve this is to clear the history table, it seems as soon as that starts to fill up for a few days (on a busy site) the downloads list will need not load and we get “There has been a critical error on this website” to which if we check the debug log it comes down to

[02-Feb-2021 11:30:45 UTC] PHP Warning: Illegal string offset ‘601937e58b9a0’ in /home/#/public_html/#/plugins/download-manager/libs/class.DownloadStats.php on line 50
[02-Feb-2021 11:30:45 UTC] PHP Fatal error: Allowed memory size of 1258291200 bytes exhausted (tried to allocate 9223372036854775840 bytes) in /home/#/public_html/#/plugins/download-manager/libs/class.DownloadStats.php on line 50
[02-Feb-2021 11:30:47 UTC] PHP Warning: Illegal string offset ‘601937e7c120f’ in /home/#/public_html/#/plugins/download-manager/libs/class.DownloadStats.php on line 50
[02-Feb-2021 11:30:47 UTC] PHP Fatal error: Allowed memory size of 1258291200 bytes exhausted (tried to allocate 6019370000032 bytes) in /home/#/public_html/#/plugins/download-manager/libs/class.DownloadStats.php on line 50
[02-Feb-2021 11:31:35 UTC] PHP Fatal error: Out of memory (allocated 492756992) (tried to allocate 60149024 bytes) in /home/#/public_html/wp-includes/wp-db.php on line 2056

I have downgraded to 3.1.11, just in case this can fix the issue until it is resolved.

I should add the site is on a dedicated VPS, has loads of mem etc… and never had this issue

UPDATE
I found the latest version is actually creating nearly 900mb of overhead in the postmeta database, having cleared that and rolled back to 3.1.08 seems to solve the issue for all the above