It seems that we need to adjust our MongoDB 4.0 build and packaging process on newer Debian based distros (e.g. Debian 9 and Ubuntu 18.04) as libcurl4 is the version of the library that the OS uses for the curl client itself and any other packages which have a libcurl dependency--whereas mongod has an explicit dependency on libcurl3. Examples of user reported issues can be seen on the user mailing list. 

More generally we should verify that our build and packaging processes always ensure that mongod depends upon and links in the default libcurl library provided by the given host OS.