This problem is not addressed in any checklist or guideline. Systematic reviews may be registered or conducted without being published, often due to a lack of statistically significant findings. These are sometimes called "zombie reviews" which are kept in the file drawer as they can be more difficult to publish. This contributes to publication bias as well as research waste.
Articles that support this problem:
Unpublished systematic reviews and financial support: a meta-epidemiological study
2017 : Bmc research notes
Reporting bias in the literature on the associations of health-related behaviors and statins with cardiovascular disease and all-cause mortality
2018 : Plos biology
More systematic reviews were registered in PROSPERO each year, but few records’ status was up-to-date
2020 : Journal of clinical epidemiology
Half of systematic reviews about pain registered in PROSPERO were not published and the majority had inaccurate status
2019 : Journal of clinical epidemiology
An international survey indicated that unpublished systematic reviews exist
2009 : Journal of clinical epidemiology
Following 411 Cochrane protocols to completion: a retrospective cohort study
2008 : Plos one
Factors predicting completion and time to publication of Cochrane reviews
2009 : Open medicine
Deficiencies in the publication and reporting of the results of systematic reviews presented at scientific medical conferences
2015 : Journal of clinical epidemiology
Following Cochrane review protocols to completion 10 years later: a retrospective cohort study and author survey
2019 : Journal of clinical epidemiology
Cochrane systematic reviews for the mental health field: is the gold standard tarnished?
2013 : Psychiatric services
The fate of urological systematic reviews registered in PROSPERO
2019 : World journal of urology
Zombie reviews taking over the PROSPERO systematic review registry. It’s time to fight back!
2019 : British journal of sports medicine
Characteristics, completion and publication of PROSPERO records in regional anesthesia for acute perioperative pain
2023 : Journal of comparative effectiveness research