Change to PHP 7.2: 0 - Using $this when not in object context

Change to PHP 7.2: 0 - Using $this when not in object context

Hi!
I administrate 3 joomshopping installtions on different websites:

Joomla is 3.8.13
Joomshopping 4.18.2
MySQL 5.6.33

If I change PHP from 7.0 to 7.2 the shops will not work in the front-end.
I get the following broswer message:

0 - Using $this when not in object context

And that is the same at all three different installations, even if I change to PHP 7.1.
Do you have any solution?

Thanks in advance.

Aw: Change to PHP 7.2: 0 - Using $this when not in object context

1. page url?
2. addon / plugins installed?

Aw: Change to PHP 7.2: 0 - Using $this when not in object context

https://www.
Payment for Usergroup 1.0.4
Addon Shipping User Group 2.2.1
Product Groups Discount 1.1.2
User groups discount for category 1.1.0

https://www.
no addons!

https://www.
Delivery Datetime 1.5.4
JoomShopping addon order gutschrift 1.2.2
Joomshopping language pack editor 1.0.4
Shop work (Country, Postal Code) 1.0.7

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Aw: Change to PHP 7.2: 0 - Using $this when not in object context

https://www.rsl-offroad.de
no addons!

ftp?
url with errors?