Illegal string offset ‘type’

Hi everybody. I am getting lots of PHP warnings on my wordpress installation and I am also seeing Internal Server Errors 500 coming up regularly.
I am using PHP 7.3 and have the latest plugin version 2.2.2 installed.

log file entries look like this:

[08-Dec-2019 11:54:51 UTC] PHP Warning:  array_key_exists() expects parameter 2 to be array, string given in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1491
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1492
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Cannot assign an empty string to a string offset in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1492
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1495
[08-Dec-2019 11:54:51 UTC] PHP Notice:  Uninitialized string offset: 0 in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1495
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1495
[08-Dec-2019 11:54:51 UTC] PHP Notice:  Uninitialized string offset: 0 in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1495
[08-Dec-2019 11:54:51 UTC] PHP Warning:  array_key_exists() expects parameter 2 to be array, string given in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1703
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1704
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Cannot assign an empty string to a string offset in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1704
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1707
[08-Dec-2019 11:54:51 UTC] PHP Notice:  Uninitialized string offset: 0 in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1707
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1707
[08-Dec-2019 11:54:51 UTC] PHP Notice:  Uninitialized string offset: 0 in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1707
[08-Dec-2019 11:54:51 UTC] PHP Warning:  array_key_exists() expects parameter 2 to be array, string given in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1891
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1892
[08-Dec-2019 11:54:51 UTC] PHP Warning:  Cannot assign an empty string to a string offset in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1892
[08-Dec-2019 11:54:52 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1895
[08-Dec-2019 11:54:52 UTC] PHP Notice:  Uninitialized string offset: 0 in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1895
[08-Dec-2019 11:54:52 UTC] PHP Warning:  Illegal string offset 'type' in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1895
[08-Dec-2019 11:54:52 UTC] PHP Notice:  Uninitialized string offset: 0 in /mnt/web414/a2/23/59365623/htdocs/WordPress_01/wp-content/plugins/responsive-lightbox/includes/class-frontend.php on line 1895

Any idea how to solve the issue?

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