Error when assembling plots with cowplot::plot_grid - r

Question

I am using the following code to produce the scatter diagram of a Redundancy Analysis (RDA). The plot is for only one species and I am conducting this analysis for two other species (I am not showing the code for the other two species as it is basically the same).
rda.plot.sap <- ggplot(df1, aes(x=RDA1, y=RDA2)) +
geom_point(aes(shape = df1[,"Enclos"], color = df1[,"Type_enclos"]), size = 2) +
geom_hline(yintercept=0) +
geom_vline(xintercept=0) +
coord_fixed() +
scale_shape_manual(values = c(1, 19)) +
scale_color_manual(values=c('#999999','#E69F00'))
rda.plot.sap <- rda.plot.sap +
geom_segment(data=df2,
aes(x=0, xend=RDA1, y=0, yend=RDA2),
color="red", arrow=arrow(length=unit(0.01,"npc")), size = 0.8) +
geom_text(data=df2,
aes(x=RDA1, y=RDA2, label=rownames(df2),
hjust=0.5*(1-sign(RDA1)) + hjust_sap_x,
vjust=0.5*(1-sign(RDA2) + vjust_sap_x)),
color="red", size=5)
rda.plot.sap <- rda.plot.sap +
geom_segment(data=df3,
aes(x=0, xend=RDA1, y=0, yend=RDA2),
color="blue", arrow=arrow(length=unit(0.01,"npc")), size = 0.8)+
geom_text(data=df3,
aes(x=RDA1, y=RDA2, label=rownames(df3),
hjust=0.5*(1-sign(RDA1)),
vjust=0.5*(1-sign(RDA2))),
color="blue", size=5)
rda.plot.sap <- rda.plot.sap +
theme(panel.background = element_blank(),
axis.title = element_text(size = 20),
axis.line.x = element_line(color="black", size = 1),
axis.line.y = element_line(color="black", size = 1),
axis.text = element_text(size = 15),
legend.title = element_blank(),
legend.text = element_text(size = 15),
legend.key=element_blank(),
legend.position = c(0.15, 0.9)) +
xlim(c(-0.6, 0.4))
rda.plot.sap <- rda.plot.sap +
xlab(paste("RDA1 (", var.rda1, " % - p = ", p.rda1, ")", sep = "")) +
ylab(paste("RDA2 (", var.rda2, " % - p = ", p.rda2, ")", sep = ""))
The code works perfectly fine, and I obtain three separate plots without any error or warnings. The problem is that when I try to assemble these three plots using the function plot_grid of the cowplot package:
final_plot <- plot_grid(rda.plot.sap, rda.plot.epi, rda.plot.het,
nrow = 1, ncol = 3, labels = c("A", "B", "C"))
I always get the same simple error :
"Error: Aesthetics must be either length 1 or the same as the data
(27): shape, colour".
Even stranger, after getting this error, if I want to run again the code of one of the individual plots (of one species only), I get the same error.
This is my first post so I hope I described the problem accurately enough. I am at a loss to understand what is going on here, so thanks in advance to whoever can help.

Answer 1

I'm not sure why, but removing the labels argument from plot_grid() usually fixes this. (You just need to add the labels to each plot individually with geom_text() or ggtitle().)

Answer 2

According to the comment found for this gist, the issue has to do with custom theme not setting the required aesthetics for plot_grid to use for the labels. See the following fix:
final_plot <- plot_grid(rda.plot.sap, rda.plot.epi, rda.plot.het,
nrow = 1, ncol = 3, labels = c("A", "B", "C"),
label_fontfamily = "Times", label_colour = "black")