error 500 after 8.1 upgrade

[sales1450]

After upgrading to 8.1, index.php produces an error 500.
"This page isn't working [ External links are visible to forum administrators only ] is currently unable to handle this request. HTTP ERROR 500"

If I revert to 8.0, everything works.

I use godaddy to host.
error_log reports:

[25-Feb-2021 18:00:37 UTC] PHP Warning:  Illegal string offset 'u404' in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 112
[25-Feb-2021 18:00:37 UTC] PHP Warning:  count(): Parameter must be an array or an object that implements Countable in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 112
[25-Feb-2021 18:00:37 UTC] PHP Warning:  Illegal string offset 'u404' in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 112
[25-Feb-2021 18:00:37 UTC] PHP Warning:  Illegal string offset 'initdir' in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 115
[25-Feb-2021 18:00:37 UTC] PHP Warning:  Invalid argument supplied for foreach() in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 117
[25-Feb-2021 18:00:37 UTC] PHP Warning:  Illegal string offset 'u404' in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 112
[25-Feb-2021 18:00:37 UTC] PHP Warning:  count(): Parameter must be an array or an object that implements Countable in /home/n8yhh1qnpz5n/public_html/generator/pages/page-l404.inc.php on line 112
[25-Feb-2021 18:01:06 UTC] PHP Warning:  count(): Parameter must be an array or an object that implements Countable in /home/n8yhh1qnpz5n/public_html/generator/pages/page-view.inc.php on line 114
[25-Feb-2021 18:20:51 UTC] PHP Warning:  count(): Parameter must be an array or an object that implements Countable in /home/n8yhh1qnpz5n/public_html/generator/pages/page-view.inc.php on line 114
[25-Feb-2021 18:21:24 UTC] PHP Warning:  count(): Parameter must be an array or an object that implements Countable in /home/n8yhh1qnpz5n/public_html/generator/pages/page-view.inc.php on line 114
[25-Feb-2021 18:25:07 UTC] PHP Parse error:  syntax error, unexpected end of file in /home/n8yhh1qnpz5n/public_html/generator/pages/class.utils.inc.php on line 102

[XML-Sitemaps Support]

Hello,

Please try to redownload and reinstall sitemap generator now.

[sales1450]

this works!
thank you