RAF is throwing error while playing video immediately after another

The ad playback with HLS stream is working fine if I play the content one by one with some time gap between each playback.

But, If I play the video without any time gap, for certain playbacks the ad is not showing and the RAF is throwing some error as No Ads VAST Response

The pod URL I'm using is https://pubads.g.doubleclick.net/gampad/ads?sz=640x480&iu=/124319096/external/ad_rule_samples&ciu_szs=300x250&ad_rule=1&impl=s&gdfp_req=1&env=vp&output=vmap&unviewed_position_start=1&cust_params=deployment%3Ddevsite%26sample_ar%3Dpremidpostoptimizedpod&cmsid=496&vid=short_onecue&correlator=