Relevant parts:
Partner represents and warrants that it shall not introduce into WhatsApp’s Systems or Infrastructure, the Sublicensed Encryption Software, or otherwise make accessible to WhatsApp any viruses or any software licensed under the General Public Licence or any similar licence (e.g. GNU Affero General Public License (AGPL), GNU General Public License (GPL), GNU Lesser General Public License (LGPL)) containing a “copyleft” requirement during performance of the Services.
Partner shall not: (i) combine Sublicensed Encryption Software with any software licensed under any version of or derivative of the GNU General Public License (e.g.; GNU Affero General Public License (AGPL), GNU General Public License (GPL), GNU Lesser General Public License (LGPL) in any manner that could cause, or could be interpreted or asserted to cause, the Sublicensed Encryption Software or any modifications to the Sublicensed Encryption Software to become subject to the terms of any version of or derivative of the GNU General Public License or other copyleft open source software
Pardon me, but would this not interfere with partners’ ability to host services via 99% of Linux-based servers?
No, running software on GPL licensed systems does not make the guest software GPL.
But, The AGPL is “infectious”, and one bit of AGPL can make your entire project subject to the AGPL. It’s a legal nightmare and many businesses outright ban the use of AGPL software.
Presumably, they’ve just blanket banned GPL to avoid any ambiguity.