Lyx BibTeX error: illegal, another bibstyle command

I’m getting the above error when including multiple child documents in a main document. Each child document has a BibTeX Bibliography. The child documents on their own don’t have errors. And if I include only a single child document in the main document there is no error. However as soon as multiple child documents are included, the error arises.

What am I doing wrong?

Attached is a screenshot of the BibTeX log:

MWE:

    lyxformat 544
begin_document
begin_header
save_transient_properties true
origin unavailable
textclass report
use_default_options true
maintain_unincluded_children false
language english
language_package default
inputencoding auto
fontencoding global
font_roman "default" "default"
font_sans "default" "default"
font_typewriter "default" "default"
font_math "auto" "auto"
font_default_family default
use_non_tex_fonts false
font_sc false
font_osf false
font_sf_scale 100 100
font_tt_scale 100 100
use_microtype false
use_dash_ligatures true
graphics default
default_output_format default
output_sync 0
bibtex_command default
index_command default
paperfontsize default
spacing single
use_hyperref false
papersize default
use_geometry false
use_package amsmath 1
use_package amssymb 1
use_package cancel 1
use_package esint 1
use_package mathdots 1
use_package mathtools 1
use_package mhchem 1
use_package stackrel 1
use_package stmaryrd 1
use_package undertilde 1
cite_engine basic
cite_engine_type default
biblio_style plain
use_bibtopic false
use_indices false
paperorientation portrait
suppress_date false
justification true
use_refstyle 1
use_minted 0
index Index
shortcut idx
color #008000
end_index
secnumdepth 3
tocdepth 3
paragraph_separation indent
paragraph_indentation default
is_math_indent 0
math_numbering_side default
quotes_style english
dynamic_quotes 0
papercolumns 1
papersides 1
paperpagestyle default
tracking_changes false
output_changes false
html_math_output 0
html_css_as_file 0
html_be_strict false
end_header

begin_body

begin_layout Standard
begin_inset CommandInset include
LatexCommand include
filename "Chapter1/Chapter1_test.lyx"

end_inset


end_layout

begin_layout Standard
begin_inset CommandInset include
LatexCommand include
filename "Chapter2/Chapter2_test.lyx"

end_inset


end_layout

end_body
end_document

That’s the master document and as soon as I include any 2 child documents with Bibliographies, I get the error.