Thanks.
My host provides for two Log File Downloads: View Access Log and View Error Log.
I assume the latter is the relevant one. I ran the 6.1 upgrade routine again and immediately downloaded the logs.
The last minute of the Error Log is:
fhithich.uk [Wed Nov 09 20:17:44 2022] [error] [client 144.76.68.17:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:17:55 2022] [error] [client 87.75.112.183:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:17:57 2022] [error] [client 35.245.82.188:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:07 2022] [error] [client 87.75.112.183:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:14 2022] [error] [client 87.75.112.183:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:14 2022] [error] [client 54.36.148.2:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:16 2022] [error] [client 10.16.12.8:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:18 2022] [error] [client 10.16.12.8:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:18 2022] [error] [client 10.16.12.8:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:22 2022] [error] [client 157.55.39.211:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:32 2022] [error] [client 87.75.112.183:0] mmap() failed: [12] Cannot allocate memory
fhithich.uk [Wed Nov 09 20:18:32 2022] [error] [client 87.75.112.183:0]
fhithich.uk [Wed Nov 09 20:18:32 2022] [error] [client 87.75.112.183:0]
fhithich.uk [Wed Nov 09 20:18:32 2022] [error] [client 87.75.112.183:0] mmap() failed: [12] Cannot allocate memory
fhithich.uk [Wed Nov 09 20:18:35 2022] [error] [client 144.76.68.17:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
fhithich.uk [Wed Nov 09 20:18:36 2022] [error] [client 64.62.252.174:0] PHP: syntax error, unexpected '(' in /home/cluster-sites/2/f/fhithich.uk/public_html/php.ini on line 1
This is all pretty meaningless to me but seems to indicate something wrong on the php.ini file.
I did manage to find and have a look at this file and it is just the one line:
<?php phpinfo(); ?>
Any further help appreciated.