Hello,
i have found it Jmeter log lots warnings like this:
2019-05-14 12:53:24,682 WARN c.h.c.r.e.LoggingCSSParseErrorHandler: [37:17] Unexpected rule '@charset': charset rule in the middle of the file is not allowed!

 We discovered that is related to autodownloaded (through HTTP Request Defaults - Revrieve All Embedded Resources) static resource css file, which is parser, i dunno why, maybe for other resources..

In file is @charset text, which confunse Jmeter.

Contain of Jmeter file:
@charset "UTF-8"; html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, font, img, ins, kbd, q, s, samp, small, strike, strong, tt, var, dl, dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td { margin: 0; padding: 0; border: 0; outline: 0; font-weight: inherit; font-style: inherit; font-size: 100%; font-family: inherit; vertical-align: baseline; } table { border-collapse: separate; border-spacing: 0; } th, td {text-align: left; font-weight: normal; vertical-align: middle; } img, iframe { border: none; text-decoration: none; vertical-align: top; } ol, ul { list-style: none; } input, textarea, select, button { font-size: 100%; font-family: inherit; } select { margin: inherit; } hr { margin: 0; padding: 0; border: 0; background-color: #000; height: 1px; } .cleaner { clear: both; height: 0; font-size: 0; overflow: hidden; display: block; } .w180 { width: 180px; } .w290 { width: 290px; } .mb0 { margin-bottom: 0 !important; } .ml0 { margin-left: 0 !important; } .pt08 { padding-top: 08px; } .fLeft { float: left !important; } .fRight { float: right !important; } .fNone { float: none !important; } .fs16 { font-size: 16px !important; } @charset "UTF-8"; html * { font-size: 100.01%; } body, input { font-size: 12px; font-family: arial, Helvetica, sans-serif; } h1 { margin: 0 0 20px 0; padding: 15px 0 0 0; font-size: 20px; font-weight: bold; position: relative; z-index: 2; } p { margin: 0 0 15px 0; line-height: 22px; color: #3b3b3b; } a { color: #005A93; text-decoration: underline; } a:hover { color: #017BC3; } a:visited { text-decoration: underline; } strong, b { font-weight: bold; } /*--INFO-BOX-------------------------------------------------*/ .infoBox { width: 960px; height: 44px; /*margin-bottom: 30px;*/ background: url("../images/info_box.jpg") 0 0 no-repeat; } .infoBox .content p { padding: 7px 30px 0 75px; margin: 0; color: #000; font-size: 12px; line-height: 16px; font-weight: bold; }

 I think that its valid response from browsers point of view.