When using a filter with a wildcard (eg. filter=name eq '*.email*') in the IoT files Search Files API, responses usually take a very long time. Without wildcards (or without filtering at all), responses are usually <1 second.
Solution
Wild cards are allowed to be used in File Search for search operations. But we would suggest avoiding beginning patterns with '*' or '?'. This would increase the iterations needed to find matching terms and slow search performance. This is the known issue in the Elastic Search which is used in File Service.
Notes