Uhhh ...
++ This page should be using theme contemporary which cannot be initialised. Falling back to the site theme boost ++
says whatever you did to change the theme, didn't take.
So one more item ... in config.php file of the active site, add the following line:
'$CFG->theme='boost';
Check your moodlecode/theme directory via anything you have to browse files. If you should see only boost, classic, and eugru directories. Any other directories like contemporary ... remove.
If successfully removed, do a query of DB like so:
mysql> select * from mdl_config_plugins where name like '%theme%';
+------+---------------+----------+------------+
| id | plugin | name | value |
+------+---------------+----------+------------+
| 1891 | theme_boost | themerev | 1568043843 |
| 1953 | theme_classic | themerev | 1568043873 |
+------+---------------+----------+------------+
2 rows in set (0.00 sec)
Notice there's only the two in that table.
Issue could also be that LDAP sending characters that the DB won't except,
In your config.php file, what does the line for 'dbcollation' say?
What that shows must match DB. 3.7 now should be running not only Innodb but character set utf8mb4 with a collation of utf8mb4_something.
run these two scripts to see (and maybe fix):
from your moodle/admin/cli directory:
php mysql_compressed_rows.php -i
You should see:
Database engine: InnoDB
innodb_file_per_table: ON
innodb_file_format: Barracuda
Run
php mysql_collation.php --list
at the tail end of output, you should see something like:
mdl_workshopform_rubric_config utf8mb4_general_ci
layout utf8mb4_general_ci
mdl_workshopform_rubric_levels utf8mb4_general_ci
definition utf8mb4_general_ci
Table collations summary for https://yourserver:
utf8mb4_general_ci: 1494
which says all tables (1494 on the site I am looking at) have utf8mb4_general_ci collations.
That collation must match what's in conflg.php.
If you need to fix,
php mysql_collation.php
shows how to fix. Read the screen and type command with options to change.
Now ... what language character set is your LDAP running? Dunno how to find that out cause I don't run LDAP.
In the set up of LDAP in your moodle:
/admin/settings.php?section=authsettingldap
It does have a setting for LDAP encoding - which, by default, is set to utf-8.
and comment under that says:
"Encoding used by the LDAP server, most likely utf-8. If LDAP v2 is
selected, Active Directory uses its configured encoding, such as cp1252
or cp1250."
Your LDAP should be version 3.
Have no idea how many users need to be sync'd, but one of them is using a character in the data being pulled into Moodle, that Moodle doesn't like.
That's all I can suggest.
Emma ... handing this one over to you! 
'SoS', Ken
