How to remove intermittent headers from data

I have a large .txt file (77,000 rows) with intermittent headers in the data (see attached picture). I'm trying to get all the numeric data into a mx3 matrix. "importdata" works great until it encounters the first intermittent head, and then it stops.

This is what I have been trying, but like I said, it stop once it reaches the first buried header

filename = 'test1.txt';
[B,delimeterOut,headerlinesOut] = importdata(filename);
Load_Time = B.data(:,1);
Load_Displacement = B.data(:,2);
Load_Force = B.data(:,3);

[Stephen23]

@Jason Shepherd: please upload a representative file by clicking the paperclip button. Note it does not have to have lots of line, but needs to represent the pertinent features of the files.

You might be interested to read this, this concept can be adapted to read files with header rows interspersed among the data:

https://www.mathworks.com/help/matlab/import_export/import-large-text-files.html

[per isakson]

"(see attached picture)" Nothing attached. You need to both [Choose File] and [Insert Image].

[per isakson]

See Import Large Text File Data in Blocks