Possible problem with corrupted keys

Schleuder web exists with HTTP-Code 500, possibly caused by a problematic key in the keyring of the list. When listing the subscribers (production.log):

... (many lines ommited)
I, [2018-02-09T13:01:25.612062 #25549]  INFO -- :   Rendered lists/_subscription_row.html.haml (22.3ms)
I, [2018-02-09T13:01:25.612548 #25549]  INFO -- :   Rendered subscriptions/_subscription.html.haml (0.2ms)
I, [2018-02-09T13:01:25.640911 #25549]  INFO -- :   Rendered application/_popup.html.haml (0.5ms)
I, [2018-02-09T13:01:25.641246 #25549]  INFO -- :   Rendered lists/_subscription_row.html.haml (29.0ms)
I, [2018-02-09T13:01:25.641483 #25549]  INFO -- :   Rendered lists/subscriptions.html.haml within layouts/application (4995.4ms)
I, [2018-02-09T13:01:25.645541 #25549]  INFO -- :   Rendered application/_navbar.html.haml (2.5ms)
I, [2018-02-09T13:01:25.646237 #25549]  INFO -- :   Rendered application/_flashes.html.haml (0.2ms)
I, [2018-02-09T13:01:25.677819 #25549]  INFO -- :   Rendered application/_list_menu.html.haml (30.4ms)
I, [2018-02-09T13:01:25.678076 #25549]  INFO -- :   Rendered application/_page_header.html.haml (31.5ms)
I, [2018-02-09T13:01:25.679771 #25549]  INFO -- :   Rendered errors/404.html.haml within layouts/application (0.2ms)
I, [2018-02-09T13:01:25.684085 #25549]  INFO -- :   Rendered application/_navbar.html.haml (2.6ms)
I, [2018-02-09T13:01:25.684684 #25549]  INFO -- :   Rendered application/_flashes.html.haml (0.1ms)
I, [2018-02-09T13:01:25.708890 #25549]  INFO -- :   Rendered application/_list_menu.html.haml (23.3ms)
I, [2018-02-09T13:01:25.709093 #25549]  INFO -- :   Rendered application/_page_header.html.haml (24.1ms)
I, [2018-02-09T13:01:25.709532 #25549]  INFO -- : Completed 500 Internal Server Error in 5235ms (ActiveRecord: 0.2ms)
F, [2018-02-09T13:01:25.713364 #25549] FATAL -- : 
ActionView::Template::Error (Failed.  Response code = 404.  Response message = Not Found.):
    1: - if @list.key.blank?
    2:   .alert.alert-warning 
    3:     %strong
    4:       This list is not functional!
  app/models/list.rb:19:in `key'
  app/views/application/_list_menu.html.haml:1:in `_app_views_application__list_menu_html_haml___3358667719338542768_47448772710740'
  app/views/application/_page_header.html.haml:4:in `_app_views_application__page_header_html_haml__3707432296185298548_47448775313180'
  app/views/layouts/application.html.haml:22:in `_app_views_layouts_application_html_haml___2233389953293821695_47448768562820'
  app/controllers/application_controller.rb:61:in `render_404'
  app/controllers/application_controller.rb:15:in `block in <class:ApplicationController>'

Questions:

• wouldnt it be better to display this key, marked as 'damaged', but continue to operated instead of going 500
• what does that tell me about the functionality of the original list - this error occured after migration of a large list to schleuder3

cheers