Import Process crashes

the import Process is crashing due to memory limit. The problem cannot be solved by increasing the memory to 10GB. So it's propably some kind of an endless loop.

www-data@mk-staging:~/mainzer-kammerspiele.de/docroot$ ../vendor/bin/drush -y -d zid pm
Using the Drush script found at /var/www/mainzer-kammerspiele.de/vendor/drush/drush/drush.launcher using pcntl_exec
Cache HIT cid: 8.1.17-commandfiles-0-a5866a9cdfa03713439f4a1557648c5a [0.01 sec, 2.69 MB]                        [debug]
....
[debug]
WD tm_ztix_import: tm_ztix_import_check_file_exists source_file: http://www.ztix.de/kammermz/gfx/hpzgfa.jpg      [debug]
[0.73 sec, 39.8 MB]
Undefined variable: file tm_ztix_import.module:928 [0.73 sec, 39.8 MB]                                          [notice]
Undefined property: stdClass::$field_performance_cust_subtitle performances.module:34 [0.91 sec, 39.94 MB]      [notice]
Undefined property: stdClass::$field_performance_custom_promo performances.module:37 [0.91 sec, 39.95 MB]       [notice]
Undefined property: stdClass::$field_performance_custom_image performances.module:40 [0.91 sec, 39.95 MB]       [notice]
Undefined property: stdClass::$field_performance_custom_body performances.module:43 [0.91 sec, 39.95 MB]        [notice]
Undefined property: stdClass::$field_performance_custom_content performances.module:46 [0.91 sec, 39.95 MB]     [notice]
Array to string conversion devel.module:567 [0.92 sec, 40.18 MB]                                                [notice]
Array to string conversion drupal.inc:91 [0.92 sec, 40.18 MB]                                                   [notice]
WD performances: Content differs. Lets save: Array [0.92 sec, 40.18 MB]                                         [notice]
Undefined property: stdClass::$field_performance_cust_location performances.module:52 [0.92 sec, 40.18 MB]      [notice]
Undefined property: stdClass::$field_performance_custom_tags performances.module:55 [0.92 sec, 40.18 MB]        [notice]
Undefined property: stdClass::$field_performance_custom_cast performances.module:58 [0.92 sec, 40.18 MB]        [notice]
Killed