Shows no ribosome-associated and endoribonuclease activities. Displays polysome-associated endoribonuclease activity towards mRNAs and rRNAs (PubMed:25996083). May play a role in RNA surveillance pathways by recognizing stalled ribosomes and triggering endonucleolytic cleavage of aberrant mRNAs (Probable). Cleaves different types of rRNAs and mRNAs in a magnesium- and manganese-dependent and ATP-independent manner. Involved in correct maturation of megakaryocytes and especially important for proplatelet extension (By similarity). C-terminally truncated SLFN14 endoribonuclease: Requires manganese and magnesium for its endoribonuclease activity. Associates with ribosomes in an ATP-independent manner (PubMed:25996083). Expressed in spleen (PubMed:19619625).