Note that processes seems to only be pronounced with /siz/ or /siːz/ when it is a plural noun. The second edition of Webster’s New International Dictionary was published in 1934, so it would appear that the pronunciation of processes with a “long e” sound in the last syllable has been around for some time. Webster’s Second International lists it as a third-choice pronunciation.“ Analyzing and documenting our processeez“, by Conrad Weisert, 7 January 2010, says

Although the pronunciation for process with a long (o), (prō ′sĕs′), is more usual in British and Canadian English, it is an acceptable variant in American English.However, because this pronunciation is not uncommon even in educated speech, it is generally considered an acceptable variant, although it still strikes some listeners as a bungled affectation. But process is not of Greek origin, and there is no etymological justification for this pronunciation of its plural. Usage Note: In recent decades there has been a tendency to pronounce the plural ending -es of processes as (-ēz), perhaps by analogy with words of Greek origin such as analysis and diagnosis.

Processes pronunciation uk