hi.
first: my english is not so good, but i will try my best.
second: i have taken over (inherited) this projekt and i am not the creator of the site.
third: the system has done an "automatic" update in february 2020 and the site was broken than. the provider DomainFactory restored the Database and Web-Folder after the "automatic" update and since then there are some problems, but somehow the site is running. i know that some tables are not "complete"? i checked some in february.

now i tried to update from 5.7.5.13 to v8 and after 10 days i am still at the start and hope you can help, otherwise i don't know what to do.
Running the site like is is not possible, because DomainFactory is going to switch of PHP <7.2. when i switch the domain to PHP 7.2, the site is also broken.

Now my upgrade-process.

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1. Site works and this is the Siteinfo:
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# concrete5 Version
Core Version - 5.7.5.13
Version Installed - 5.7.5.13
Database Version - 20160615000000

# concrete5 Packages
Easy Image Slider (1.0.1), Table Block (0.9.5)

# concrete5 Overrides
Here are many urls ike "blocks/downloads_block/editmask.php" or "themes/clientName/image/nameOfCustomer.png". Don't know if the data is to private or needed to help me

# concrete5 Cache Settings
Block Cache - Off
Overrides Cache - Off
Full Page Caching - Off
Full Page Cache Lifetime - Every 90 minutes.

# Server Software
Apache/2.4.41

# Server API
cgi-fcgi

# PHP Version
7.0.32

# PHP Extensions
bcmath, bz2, calendar, cgi-fcgi, Core, ctype, curl, date, dba, dom, exif, fileinfo, filter, ftp, gd, gettext, hash, iconv, imap, json, libxml, mbstring, mcrypt, mysqli, mysqlnd, openssl, pcntl, pcre, PDO, pdo_mysql, pdo_sqlite, pgsql, Phar, posix, Reflection, session, SimpleXML, soap, SPL, sqlite3, standard, tokenizer, wddx, xml, xmlreader, xmlwriter, xsl, zip, zlib

# PHP Settings
max_execution_time - 180
log_errors_max_len - 1024
max_file_uploads - 20
max_input_nesting_level - 64
max_input_time - -1
max_input_vars - 1000
memory_limit - 100M
post_max_size - 8M
sql.safe_mode - Off
upload_max_filesize - 8M
mysqli.max_links - Unlimited
mysqli.max_persistent - Unlimited
pcre.backtrack_limit - 1000000
pcre.recursion_limit - 100000
pgsql.max_links - Unlimited
pgsql.max_persistent - Unlimited
session.cache_limiter - <i>no value</i>
session.gc_maxlifetime - 1440
soap.wsdl_cache_limit - 5

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2. Symlink because of multiple instances
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I have 3 Instances (Sites) of Concrete 5 CMS. So i use one Folder "Conrete5Core" and have 3 Folders. One each Site. The reason is, that i don't have to manage blocks&similar for each site individually, because same client.
From this folders i have a Symlink to the Core-Concrete-Folder like "concrete5-8.5.4". so long this settings are working for "concrete--5.7.5.13" at the time.

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3. Copying concrete 8.5.4 into concrete-Folder on Core
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Now i put the folder "concrete5-8.5.4" into the "concrete5core/updates/" - folder and change the symlink to the new Version. The Updatefolder is recognized from the system and i klick on "Aktualisierung installieren" (picture)

than it stops the installing an i get errors like this:
-The DQL alias 'r' contains an entity of an inheritance hierarchy with an empty discriminator value. This means that the database contains inconsistent data with an empty discriminator value in a table row.

-An exception occurred while executing 'ALTER TABLE atSelectedTopics ADD avTreeTopicNodeID INT UNSIGNED AUTO_INCREMENT NOT NULL, ADD treeNodeID INT UNSIGNED NOT NULL, DROP TopicNodeID, CHANGE avID avID INT UNSIGNED DEFAULT NULL': SQLSTATE[42000]: Syntax error or access violation: 1075 Incorrect table definition; there can be only one auto column and it must be defined as a key

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in the last 10 days i tried many issues. i don't know all at the time. But change folder proxies to old files, take the database before the update and have edited some php-files recommendet.
and the other question is, can up update with php 7.0.32 to version 8.5.4 and switch than to php 7.3?

sorry for my bad englisch. hope u can help me. my last chance. thx