REST API - "Request Entity too large" error on uploading image larger than ~50KB


on some groupshare servers, I reveive a "413 - Request entity too large " error message when trying to upload an image larger than ~50kb through the GroupShare REST API (/multiterm/api/1.0/termbases/TERMBASE/multimedia). GS is on version  14.2.47996.9 - SR1 CU9

On some other servers (e.g. 14.2.32756.8 - SR1 CU8) the size is not a problem. 

Has anyone met this issue before? How can I solve this?